PATENT ABSTRACT
A mobile telecommunications device comprising: a first transmitter for transmitting signals over a mobile telephony system, and a first receiver for receiving signals from a mobile telephony system; a first monochrome image sensor device for sensing coded data and for outputting raw data based on said sensed data; and a transmitter controller operable to control the first transmitter to transmit output data based at least partially on said sensed data via the mobile telephony system to a computer system.

PATENT DESCRIPTION
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation-in-part of U.S. application Ser. No. 10/309,185 filed on Dec. 4, 2002, which is a continuation of U.S. Ser. No. 09/693,335 filed on Oct. 20, 2000 now issued U.S. Pat. No. 6,550,997, the entire contents of which are now incorporated by reference. 

   FIELD OF INVENTION 
   The present invention relates to Netpage enabled mobile devices. The invention has primarily been designed for use in a mobile device such as a mobile telecommunications device (i.e. a mobile phone) that incorporates a printer, and will be described with reference to such an application. However, it will be appreciated by those skilled in the art that the invention can be used with other types of portable device, or even non-portable devices. 
   CO-PENDING APPLICATIONS 
   The following applications have been filed by the Applicant simultaneously with the present application: 
                                                   11/124158   11/124196   11/124199   11/124162   11/124202   11/124197       11/124154   11/124198   11/124153   11/124151   11/124160   11/124192       11/124175   11/124163   11/124149   11/124152   11/124173   11/124155       11/124157   11/124174   11/124194   11/124164   11/124200   11/124195       11/124166   11/124150   11/124172   11/124165   11/124186   11/124185       11/124184   11/124182   11/124201   11/124171   11/124181   11/124161       11/124156   11/124191   11/124159   11/124175   11/124188   11/124170       11/124187   11/124189   11/124190   11/124180   11/124193   11/124183       11/124178   11/124177   11/124148   11/124167   11/124179   11/124169                    
The disclosures of these co-pending applications are incorporated herein by reference.
 
   CROSS REFERENCES 
   The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference. 
   
     
       
             
             
             
             
             
             
           
         
             
                 
             
           
           
             
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   BACKGROUND OF INVENTION 
   The Assignee has developed mobile phones, personal data assistants (PDAs) and other mobile telecommunication devices, with the ability to print hard copies of images or information stored or accessed by the device (see for example, U.S. Pat. No. 6,405,055 , filed on Nov. 9, 1999). Likewise, the Assignee has also designed digital cameras with the ability to print captured images with an inbuilt printer (see for example, U.S. Pat. No. 6,750,901. As the prevalence of mobile telecommunications devices with digital cameras increases, the functionality of these devices is further enhanced by the ability to print hard copies. 
   As these devices are portable, they must be compact for user convenience. Accordingly, any printer incorporated into the device needs to maintain a small form factor. Also, the additional load on the battery should be as little as possible. Furthermore, the consumables (ink and paper etc) should be relatively inexpensive and simple to replenish. It is these factors that strongly influence the commercial success or otherwise of products of this type. With these basic design imperatives in mind, there are on-going efforts to improve and refine the functionality of these devices. 
   The Assignee of the present invention has also developed the Netpage system for enabling interaction with computer software using a printed interface and a proprietary stylus-shaped sensing device. 
   As described in detail in U.S. Pat. No. 6,792,165, filed on Nov. 25, 2000 and U.S. patent application Ser. No. 10/778,056, filed on Feb. 17, 2004 a Netpage pen captures, identifies and decodes tags of coded data printed onto a surface such as a page. In a preferred Netpage implementation, each tag encodes a position and an identity of the document. By decoding at least one of the tags and transmitting the position (or a refined version of the position, representing a higher resolution position of the pen) and identity referred to by the decoded tag, a remote computer can determine an action to perform. Such actions can include, for example, causing information to be saved remotely for subsequent retrieval, downloading of a webpage for printing or display via a computer, bill payment or even the performance of handwriting recognition based on a series of locations of the Netpage pen relative to the surface. These and other applications are described in many of the Netpage-related applications cross-referenced by the present application. 
   SUMMARY OF INVENTION 
   In a first aspect the present invention provides a mobile telecommunications device comprising:
         a first transmitter for transmitting signals over a mobile telephony system, and   a first receiver for receiving signals from a mobile telephony system;   a first monochrome image sensor device for sensing coded data and for outputting raw data based on said sensed data; and   a transmitter controller operable to control the first transmitter to transmit output data based at least partially on said sensed data via the mobile telephony system to a computer system.       

   Optionally the mobile telecommunications device further comprising a sylus allowing the user to use the mobile telecommunications device as a writing or drawing device. 
   Optionally the first monochrome image sensor device is positioned on the stylus. 
   Optionally the stylus has a printhead tip with an array of nozzles to effect the writing or drawing. 
   Optionally the mobile telecommunications device further comprising a printer mechanism with a pagewidth printhead for printing on a media substrate, the printhead positioned adjacent a media feed path through the device. 
   Optionally the printer mechanism is adapted to receive document data and to print an interface onto a surface, the interface being at least partially based on the document data, the document data including identity data indicative of at least one identity, the identity being associated with a region of the interface, the interface including coded data. 
   Optionally the mobile telecommunications device further comprising at least one ink reservoir wherein the printhead tip in the stylus and the printer mechanism share the at least one ink reservoir. 
   Optionally the mobile telecommunications device further comprising a second transmitter and a second receiver adapted to transmit data to and to receive data from one or more monochrome image sensor devices, the sensor devices transmitting data. 
   Optionally the mobile telecommunications device further comprising a second transmitter and a second receiver adapted to transmit data to and to receive data from one or more monochrome image sensor devices, the sensor devices transmitting data. 
   Optionally the mobile telecommunications device further comprising a transmitter controller adapted to cause the mobile telephone unit to transmit data based on the first data to a computer system via the first transmitter. 
   Optionally the printer mechanism further comprises a capper assembly movable between a capped position covering the nozzles and an uncapped position spaced from the nozzles; wherein, the capper assembly is held in the uncapped position by the media such that it moves to the capped position upon disengagement with the media. 
   Optionally the sheet of media substrate is encoded with the coded data and the print engine controller uses a sensor to determine the position of the sheet relative to the printhead. 
   Optionally the mobile telecommunications device further comprising a media feed roller for feeding the media past the printhead. 
   Optionally the media substrate is a sheet and the trailing edge of the sheet disengages from the media feed roller before it is printed and is projected past the printhead by its momentum. 
   Optionally the capper assembly lightly grips the sheet after it has been printed so that it partially extends from the mobile telecommunications device in readiness for manual collection. 
   Optionally the capper assembly moves out of the capped position and toward the uncapped position upon engagement with the leading edge of the sheet. 
   Optionally the printhead is incorporated into a cartridge that further comprises a print media feed path for directing the print media past the printhead in a feed direction during printing, and a drive mechanism for driving the print media past the printhead for printing. 
   Optionally the printhead has an array of ink ejection nozzles and is incorporated into a cartridge that further comprises at least one ink reservoir for supplying ink to the printhead for ejection by the nozzles, each of the at least one ink reservoirs including at least one absorbent structure for inducing a negative hydrostatic pressure in the ink at the nozzles, and a capping mechanism for capping the printhead when not in use. 
   Optionally the mobile telecommunications device further comprising a drive shaft with a media engagement surface for feeding a media substrate along a feed path; and,
     a media guide adjacent the drive shaft for biasing the media substrate against the media engagement surface.   

   Optionally the mobile telecommunications device further comprising:
     a drive shaft for feeding the sheet of media substrate past the printhead; wherein during use,   the sheet disengages from the drive shaft before completion of its printing such that the trailing edge of the sheet projects past the printhead by momentum to complete its printing.
 
Terminology
   

   Mobile device: When used herein, the phrase “mobile device” is intended to cover all devices that by default operate on a portable power source such as a battery. As well as including the mobile telecommunications device defined above, mobile devices include devices such as cameras, non telecommunications-enabled PDAs and hand-held portable game units. “Mobile devices” implicitly includes “mobile telecommunications devices”, unless the converse is clear from the context. 
   Mobile telecommunications device: When used herein, the phrase “mobile telecommunications device” is intended to cover all forms of device that enable voice, video, audio and/or data transmission and/or reception. Typical mobile telecommunications devices include:
         GSM and 3G mobile phones (cellphones) of all generational and international versions, whether or not they incorporate data transmission capabilities; and   PDAs incorporating wireless data communication protocols such as GPRS/EDGE of all generational and international versions.       

   M-Print: The assignee&#39;s internal reference for a mobile printer, typically incorporated in a mobile device or a mobile telecommunications device. Throughout the specification, any reference made to the M-Print printer is intended to broadly include the printing mechanism as well as the embedded software which controls the printer, and the reading mechanism(s) for the media coding. 
   M-Print mobile telecommunications device: a mobile telecommunications device incorporating a Memjet printer. 
   Netpage mobile telecommunications device: a mobile telecommunications device incorporating a Netpage-enabled Memjet printer and/or a Netpage pointer. 
   Throughout the specification, the blank side of the medium intended to be printed on by the M-Print printer is referred to as the front side. The other side of the medium, which may be pre-printed or blank, is referred to as the back side. 
   Throughout the specification, the dimension of the medium parallel to the transport direction is referred to as the longitudinal dimension. The orthogonal dimension is referred to as the lateral dimension. 
   Furthermore, where the medium is hereafter referred to as a card, it should be understood that this is not meant to imply anything specific about the construction of the card. It may be made of any suitable material including paper, plastic, metal, glass and so on. Likewise, any references to the card having been pre-printed, either with graphics or with the media coding itself, is not meant to imply a particular printing process or even printing per se. The graphics and/or media coding can be disposed on or in the card by any suitable means. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic representation of the modular interaction in a printer/mobile phone; 
       FIG. 2  is a schematic representation of the modular interaction in a tag sensor/mobile phone; 
       FIG. 3  is a schematic representation of the modular interaction in a printer/tag sensor/mobile phone; 
       FIG. 4  is a more detailed schematic representation of the architecture within the mobile phone of  FIG. 3 ; 
       FIG. 5  is a more detailed schematic representation of the architecture within the mobile phone module of  FIG. 4 ; 
       FIG. 6  is a more detailed schematic representation of the architecture within the printer module of  FIG. 4 ; 
       FIG. 7  is a more detailed schematic representation of the architecture within the tag sensor module of  FIG. 4 ; 
       FIG. 8  is a schematic representation of the architecture within a tag decoder module for use instead of the tag sensor module of  FIG. 4 ; 
       FIG. 9  is an exploded perspective view of a ‘candy bar’ type mobile phone embodiment of the present invention; 
       FIG. 10  is a partially cut away front and bottom perspective of the embodiment shown in  FIG. 9 ; 
       FIG. 11  is a partially cut away rear and bottom perspective of the embodiment shown in  FIG. 9 ; 
       FIG. 12  is a front elevation of the embodiment shown in  FIG. 9  with a card being fed into its media entry slot; 
       FIG. 13  is a cross section view taken along line A-A of  FIG. 12 ; 
       FIG. 14  is a cross section view taken along line A-A of  FIG. 12  with the card emerging from the media exit slot of the mobile phone; 
       FIG. 15  is a schematic representation of a first mode of operation of MoPEC; 
       FIG. 16  is a schematic representation of a second mode of operation of MoPEC; 
       FIG. 17  is a schematic representation of the hardware components of a MoPEC device; 
       FIG. 18  shows a simplified UML diagram of a page element; 
       FIG. 19  is a top perspective of the cradle assembly and piezoelectric drive system; 
       FIG. 20  is a bottom perspective of the cradle assembly and piezoelectric drive system; 
       FIG. 21  is a bottom perspective of the print cartridge installed in the cradle assembly; 
       FIG. 22  is a bottom perspective of the print cartridge removed from the cradle assembly; 
       FIG. 23  is a perspective view of a print cartridge for an M-Print device; 
       FIG. 24  is an exploded perspective of the print cartridge shown in  FIG. 23 ; 
       FIG. 25  is a circuit diagram of a fusible link on the printhead IC; 
       FIG. 26  is a circuit diagram of a single fuse cell; 
       FIG. 27  is a schematic overview of the printhead IC and its connection to MoPEC; 
       FIG. 28  is a schematic representation showing the relationship between nozzle columns and dot shift registers in the CMOS blocks of  FIG. 27 ; 
       FIG. 29  shows a more detailed schematic showing a unit cell and its relationship to the nozzle columns and dot shift registers of  FIG. 28 ; 
       FIG. 30  shows a circuit diagram showing logic for a single printhead nozzle; 
       FIG. 31  is a schematic representation of the physical positioning of the odd and even nozzle rows; 
       FIG. 32  shows a schematic cross-sectional view through an ink chamber of a single bubble forming type nozzle with a bubble nucleating about heater element; 
       FIG. 33  shows the bubble growing in the nozzle of  FIG. 32 ; 
       FIG. 34  shows further bubble growth within the nozzle of  FIG. 32 ; 
       FIG. 35  shows the formation of the ejected ink drop from the nozzle of  FIG. 32 ; 
       FIG. 36  shows the detachment of the ejected ink drop and the collapse of the bubble in the nozzle of  FIG. 32 ; 
       FIG. 37  is a perspective showing the longitudinal insertion of the print cartridge into the cradle assembly; 
       FIG. 38  is a lateral cross section of the print cartridge inserted into the cradle assembly; 
       FIGS. 39 to 48  are lateral cross sections through the print cartridge showing the decapping and capping of the printhead; 
       FIG. 49  is an enlarged partial sectional view of the end of the print cartridge indicated by the dotted line in  FIG. 51B ; 
       FIG. 50  is a similar sectional view with the locking mechanism rotated to the locked position; 
       FIG. 51A  is an end view of the print cartridge with a card partially along the feed path; 
       FIG. 51B  is a longitudinal section of the print cartridge through A-A of  FIG. 51A ; 
       FIG. 52  is a partial enlarged perspective of one end the print cartridge with the capper in the capped position; 
       FIG. 53  is a partial enlarged perspective of one end the print cartridge with the capper in the uncapped position; 
       FIG. 54  shows the media coding on the ‘back-side’ of the card with separate clock and data tracks; 
       FIG. 55  is a block diagram of an M-Print system that uses media with separate clock and data tracks; 
       FIG. 56  is a simplified circuit diagram for an optical encoder; 
       FIG. 57  is a block diagram of the MoPEC with the clock and data inputs; 
       FIG. 58  is a block diagram of the optional edge detector and page sync generator for the M-Print system of  FIG. 55 ; 
       FIG. 59  is a block diagram of a MoPEC that uses media with a pilot sequence in the data track to generate a page sync signal; 
       FIG. 60  is a schematic representation of the position of the encoders along media feed path; 
       FIG. 61  shows the ‘back-side’ of a card with a self clocking data track; 
       FIG. 62  is a block diagram of the decoder for a self clocking data track; 
       FIG. 63  is a block diagram of the phase lock loop synchronization of the dual clock track sensors; 
       FIG. 64  shows the dual phase lock loop signals at different phases of the media feed; 
       FIG. 65  is a block diagram of the Kip encoding layers; 
       FIG. 66  is a schematic representation of the Kip frame structure; 
       FIG. 67  is a schematic representation of an encoded frame with explicit clocking; 
       FIG. 68  is a schematic representation of an encoded frame with implicit clocking; 
       FIG. 69  shows Kip coding marks and spaces that are nominally two dots wide; 
       FIG. 70  is a schematic representation of the extended Kip frame structure; 
       FIG. 71  shows the data symbols and the redundancy symbols of the Reed-Solomon codeword layout; 
       FIG. 72  shows the interleaving of the data symbols of the Reed-Solomon codewords; 
       FIG. 73  shows the interleaving of the redundancy symbols of the Reed-Solomon codewords; 
       FIG. 74  shows the structure of a single Netpage tag; 
       FIG. 75  shows the structure of a single symbol within a Netpage tag; 
       FIG. 76  shows an array of nine adjacent symbols; 
       FIG. 77  shows the ordering of the bits within the symbol; 
       FIG. 78  shows a single Netpage tag with every bit set; 
       FIG. 79  shows a tag group of four tags; 
       FIG. 80  shows the tag groups repeated in a continuous tile pattern; 
       FIG. 81  shows the contiguous tile pattern of tag groups, each with four different tag types; 
       FIG. 82  is an architectural overview of a Netpage enabled mobile phone within the broader Netpage system; 
       FIG. 83  shows an architectural overview of the mobile phone microserver as a relay between the stylus and the Netpage server; 
       FIG. 84  is a perspective of a Netpage enabled mobile phone with the rear moulding removed; 
       FIG. 85  is a partial enlarged perspective of the phone shown in  FIG. 140  with the Netpage clicker partially sectioned; 
       FIG. 86  is a system level diagram of the Jupiter monolithic integrated circuit; 
       FIG. 87  is a simplified circuit diagram of the Ganymede image sensor and analogue to digital converter; 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Mobile Telecommunications Device Overview 
   Whilst the main embodiment includes both Netpage and printing functionality, only one or the other of these features is provided in other embodiments. 
   One such embodiment is shown in  FIG. 1 , in which a mobile telecommunications device in the form of a mobile phone  1  (also known as a “cellphone”) includes a mobile phone module  2  and a printer module  4 . The mobile phone module is configured to send and receive voice and data via a telecommunications network (not shown) in a conventional manner known to those skilled in the art. The printer module  4  is configured to print a page  6 . Depending upon the particular implementation, the printer module  4  can be configured to print the page  6  in color or monochrome. 
   The mobile telecommunications device can use any of a variety of known operating systems, such as Symbian (with UIQ and Series 60 GUIs), Windows Mobile, PalmOS, and Linux. 
   In the preferred embodiment (described in more detail below), the print media is pre-printed with tags, and the printer module  4  prints visible information onto the page  6  in registration with the tags. In other embodiments, Netpage tags are printed by the printer module onto the page  6  along with the other information. The tags can be printed using either the same visible ink as used to print visible information, or using an infrared or other substantially invisible ink. 
   The information printed by the printer module  4  can include user data stored in the mobile phone  1  (including phonebook and appointment data) or text and images received via the telecommunications network or from another device via a communication mechanism such as Bluetooth™ or infrared transmission. If the mobile phone  1  includes a camera, the printer module  4  can be configured to print the captured images. In the preferred form, the mobile phone module  2  provides at least basic editing capabilities to enable cropping, filtering or addition of text or other image data to the captured image before printing. 
   The configuration and operation of the printer module  4  is described in more detail below in the context of various types of mobile telecommunication device that incorporate a printhead. 
     FIG. 2  shows another embodiment of a mobile telecommunications device, in which the printer module  4  is omitted, and a Netpage tag sensor module  8  is included. The Netpage module  8  enables interaction between the mobile phone  1  and a page  10  including Netpage tags. The configuration and operation of the Netpage pointer in a mobile phone  1  is described in more detail below. Although not shown, the mobile phone  1  with Netpage module  8  can include a camera. 
     FIG. 3  shows a mobile phone  1  that includes both a printer module  4  and a Netpage tag sensor module  8 . As with the embodiment of  FIG. 2 , the printer module  4  can be configured to print tagged or untagged pages. As shown in  FIG. 3 , where tagged pages  10  are produced (and irrespective of whether the tags were pre-printed or printed by the printer module  4 ), the Netpage tag sensor module  8  can be used to interact with the resultant printed media. 
   A more detailed architectural view of the mobile phone  1  of  FIG. 3  is shown in  FIG. 4 , in which features corresponding to those shown in  FIG. 3  are indicated with the same reference numerals. It will be appreciated that  FIG. 4  deals only with communication between various electronic components in the mobile telecommunications device and omits mechanical features. These are described in more detail below. 
   The Netpage tag sensor module  8  includes a monolithically integrated Netpage image sensor and processor  12  that captures image data and receives a signal from a contact switch  14 . The contact switch  14  is connected to a nib (not shown) to determine when the nib is pressed into contact with a surface. The sensor and processor  12  also outputs a signal to control illumination of an infrared LED  16  in response to the stylus being pressed against the surface. 
   The image sensor and processor  12  outputs processed tag information to a Netpage pointer driver  18  that interfaces with the phone operating system  20  running on the mobile telecommunications device&#39;s processor (not shown). 
   Output to be printed is sent by the phone operating system  20  to a printer driver  22 , which passes it on to a MoPEC chip  24 . The MoPEC chip processes the output to generate dot data for supply to the printhead  26 , as described in more detail below. The MoPEC chip  24  also receives a signal from a media sensor  28  indicating when the media is in position to be printed, and outputs a control signal to a media transport  30 . 
   The printhead  26  is disposed within a replaceable cartridge  32 , which also includes ink  34  for supply to the printhead. 
   Mobile Telecommunications Device Module 
     FIG. 5  shows the mobile phone module  2  in more detail. The majority of the components other than those directly related to printing and Netpage tag sensing are standard and well known to those in the art. Depending upon the specific implementation of the mobile phone  1 , any number of the illustrated components can be included as part of one or more integrated circuits. 
   Operation of, and communication between, the mobile phone module  2  components is controlled by a mobile phone controller  36 . The components include:
         mobile radio transceiver  38  for wireless communication with a mobile telecommunications network;   program memory  40  for storing program code for execution on the mobile phone controller  36 ;   working memory  42  for storing data used and generated by the program code during execution. Although shown as separate from the mobile phone controller  36 , either or both memories  40  and  42  may be incorporated in the package or silicon of the controller;   keypad  44  and buttons  46  for accepting numerical and other user input;   touch sensor  48  which overlays display  50  for accepting user input via a stylus or fingertip pressure;   removable memory card  52  containing non-volatile memory  54  for storing arbitrary user data, such as digital photographs or files;   local area radio transceiver  56 , such as a Bluetooth™ transceiver;   GPS receiver  58  for enabling determination of the location of the mobile telecommunications device (alter-natively the phone may rely on mobile network mechanisms for determining its location);   microphone  60  for capturing a user&#39;s speech;   speaker  62  for outputting sounds, including voice during a phone call;   camera image sensor  64  including a CCD for capturing images;   camera flash  66 ;   power manager  68  for monitoring and controlling power consumption of the mobile telecommunications device and its components; and   SIM (subscriber Identity Module) card  70  including SIM  72  for identifying the subscriber to mobile networks.       

   The mobile phone controller  36  implements the baseband functions of mobile voice and data communications protocols such as GSM, GSM modem for data, GPRS and CDMA, as well as higher-level messaging protocols such as SMS and MMS. 
   The one or more local-area radio transceivers  56  enable wireless communication with peripherals such as headsets and Netpage pens, and hosts such as personal computers. The mobile phone controller  36  also implements the baseband functions of local-area voice and data communications protocols such as IEEE 802.11, IEEE 802.15, and Bluetooth™. 
   The mobile phone module  2  may also include sensors and/or motors (not shown) for electronically adjusting zoom, focus, aperture and exposure in relation to the digital camera. 
   Similarly, as shown in  FIG. 6 , components of the printer module  4  include:
         print engine controller (PEC)  74  in the form of a MoPEC device;   program memory  76  for storing program code for execution by the print engine controller  74 ;   working memory  78  for storing data used and generated by the program code during execution by the print engine controller  74 ; and   a master QA chip  80  for authenticating printhead cartridge  32  via its QA chip  82 .       

   Whilst the printhead cartridge in the preferred form includes the ink supply  34 , the ink reservoirs can be housed in a separate cartridge in alternative embodiments. 
     FIG. 7  shows the components of the tag sensor module  8 , which includes a CMOS tag image processor  74  that communicates with image memory  76 . A CMOS tag image sensor  78  sends captured image data to the processor  74  for processing. The contact sensor  14  indicates when a nib (not shown) is brought into contact with a surface with sufficient force to close a switch within the contact sensor  14 . Once the switch is closed, the infrared LED  16  illuminates the surface, and the image sensor  78  captures at least one image and sends it to the image processor  74  for processing. Once processed (as described below in more detail), image data is sent to the mobile phone controller  36  for decoding. 
   In an alternative embodiment, shown in  FIG. 8 , the tag sensor module  8  is replaced by a tag decoder module  84 . The tag decoder module  80  includes all the elements of the tag sensor module  8 , but adds a hardware-based tag decoder  86 , as well as program memory  88  and working memory  90  for the tag decoder. This arrangement reduces the computational load placed on the mobile phone controller, with a corresponding increase in chip area compared to using the tag sensor module  8 . 
   The Netpage sensor module can be incorporated in the form of a Netpage pointer, which is a simplified Netpage pen suitable mostly for activating hyperlinks. It preferably incorporates a non-marking stylus in place of the pen&#39;s marking nib (described in detail later in the specification); it uses a surface contact sensor in place of the pen&#39;s continuous force sensor; and it preferably operates at a lower position sampling rate, making it unsuitable for capturing drawings and hand-writing. A Netpage pointer is less expensive to implement than a Netpage pen, and tag image processing and tag decoding can potentially be performed by software without hardware support, depending on sampling rate. 
   The various aspects of the invention can be embodied in any of a number of mobile telecommunications device types. Several different devices are described here, but in the interests of brevity, the detailed description will concentrate on the mobile telecommunications device embodiment. 
   Mobile Phone 
   One preferred embodiment is the non-Netpage enabled ‘candy bar’ mobile telecommunications device in the form of a mobile phone shown in  FIGS. 9 to 14 . A Netpage enabled version is described in a later section of this specification. 
   While a candy bar style phone is described here, it could equally take the form of a “flip” style phone, which includes a pair of body sections that are hinged to each other. Typically, the display is disposed on one of the body sections, and the keypad is disposed on the other, such that the display and keypad are positioned adjacent to each other when the device is in the closed position. 
   In further embodiments, the device can have two body sections that rotate or slide relative to each other. Typically, the aim of these mechanical relationships between first and second body sections is to protect the display from scratches and/or the keypad from accidental activation. 
   Photo printing is considered one of the most compelling uses of the mobile Memjet printer. A preferred embodiment of the invention therefore includes a camera, with its attendant processing power and memory capacity. 
   The elements of the mobile telecommunications device are best shown in  FIG. 9 , which (for clarity) omits minor details such as wires and hardware that operatively connect the various elements of the mobile telecommunications device together. The wires and other hardware will be well known to those skilled in the art. 
   The mobile phone  100  comprises a chassis moulding  102 , a front moulding  104  and a rear cover moulding  106 . A rechargeable battery  108 , such as a lithium ion or nickel metal hydride battery, is mounted to the chassis moulding  102  and covered by the rear cover moulding  106 . The battery  108  powers the various components of the mobile phone  100  via battery connector  276  and the camera and speaker connector  278 . 
   The front moulding  104  mounts to the chassis to enclose the various components, and includes numerical interface buttons  136  positioned in vertical rows on each side of the display  138 . A multi-directional control pad  142  and other control buttons  284  enable menu navigation and other control inputs. A daughterboard  280  is mounted to the chassis moulding  102  and includes a directional switch  286  for the multi directional control pad  142 . 
   The mobile telecommunications device includes a cartridge access cover  132  that protects the interior of the mobile telecommunications device from dust and other foreign objects when a print cartridge  148  is not inserted in the cradle  124 . 
   An optional camera module  110  is also mounted to the chassis moulding  102 , to enable image capture through a hole  112  in the rear cover moulding  106 . The camera module  110  includes a lens assembly and a CCD image sensor for capturing images. A lens cover  268  in the hole  112  protects the lens of the camera module  110 . The rear cover moulding  106  also includes an inlet slot  228  and an outlet slot  150  through which print media passes. 
   The chassis moulding  102  supports a data/recharge connector  114 , which enables a proprietary data cable to be plugged into the mobile telecommunications device for uploading and downloading data such as address book information, photographs, messages, and any type of information that might be sent or received by the mobile telecommunications device. The data/recharge connector  114  is configured to engage a corresponding interface in a desktop stand (not shown), which holds the mobile telecommunications device in a generally upright position whilst data is being sent or received by the mobile telecommunications device. The data/recharge connector also includes contacts that enable recharging of the battery  108  via the desktop stand. A separate recharge socket  116  in the data/recharge connector  114  is configured to receive a complimentary recharge plug for enabling recharging of the battery when the desktop stand is not in use. 
   A microphone  170  is mounted to the chassis moulding  102  for converting sound, such as a user&#39;s voice, into an electronic signal to be sampled by the mobile telecommunications device&#39;s analog to digital conversion circuitry. This conversion is well known to those skilled in the art and so is not described in more detail here. 
   A SIM (Subscriber Identity Module) holder  118  is formed in the chassis moulding  102 , to receive a SIM card  120 . The chassis moulding is also configured to support a print cartridge cradle  124  and a drive mechanism  126 , which receive a replaceable print cartridge  148 . These features are described in more detail below. 
   Another moulding in the chassis moulding  102  supports an aerial (not shown) for sending and receiving RF signals to and from a mobile telecommunications network. 
   A main printed circuit board (PCB)  130  is supported by the chassis moulding  102 , and includes a number of momentary pushbuttons  132 . The various integrated and discrete components that support the communications and processing (including printing processing) functions are mounted to the main PCB, but for clarity are not shown in the diagram. 
   A conductive elastomeric overlay  134  is positoned on the main PCB  130  beneath the keys  136  on the front moulding  104 . The elastomer incorporates a carbon impregnated pill on a flexible profile. When one of the keys  136  is pressed, it pushes the carbon pill to a 2-wire open circuit pattern  132  on the PCB surface. This provides a low impedance closed circuit. Alternatively, a small dome is formed on the overlay corresponding to each key  132 . Polyester film is screen printed with carbon paint and used in a similar manner to the carbon pills. Thin adhesive film with berrylium copper domes can also be used. 
   A loudspeaker  144  is installed adjacent apertures  272  in the front moulding  104  to enable a user to hear sound such as voice communication and other audible signals. 
   A color display  138  is also mounted to the main PCB  130 , to enable visual feedback to a user of the mobile telecommunications device. A transparent lens moulding  146  protects the display  138 . In one form, the transparent lens is touch-sensitive (or is omitted and the display  138  is touch sensitive), enabling a user to interact with icons and input text displayed on the display  138 , with a finger or stylus. 
   A vibration assembly  274  is also mounted to the chassis moulding  102 , and includes a motor that drives an eccentrically mounted weight to cause vibration. The vibration is transmitted to the chassis  102  and provides tactile feedback to a user, which is useful in noisy environments where ringtones are not audible. 
   MoPEC—High Level 
   Documents to be printed must be in the form of dot data by the time they reach the printhead. 
   Before conversion to dot data, the image is represented by a relatively high spatial resolution bilevel component (for text and line art) and a relatively low spatial resolution contone component (for images and background colors). The bilevel component is compressed in a lossless format, whilst the contone component is compressed in accordance with a lossy format, such as JPEG. 
   The preferred form of MoPEC is configurable to operate in either of two modes. In the first mode, as shown in  FIG. 15 , an image to be printed is received in the form of compressed image data. The compressed image data can arrive as a single bundle of data or as separate bundles of data from the same or different sources. For example, text can be received from a first remote server and image data for a banner advertisement can be received from another. Alternatively, either or both of the forms of data can be retrieved from local memory in the mobile device. 
   Upon receipt, the compressed image data is buffered in memory buffer  650 . The bilevel and contone components are decompressed by respective decompressors as part of expand page step  652 . This can either be done in hardware or software, as described in more detail below. The decompressed bilevel and contone components are then buffered in respective FIFOs  654  and  656 . 
   The decompressed contone component is halftoned by a halftoning unit  658 , and a compositing unit  660  then composites the bilevel component over the dithered contone component. Typically, this will involve compositing text over images. However, the system can also be run in stencil mode, in which the bilevel component is interpreted as a mask that is laid over the dithered contone component. Depending upon what is selected as the image component for the area in which the mask is being applied, the result can be text filled with the underlying image (or texture), or a mask for the image. The advantage of stencil mode is that the bilevel component is not dithered, enabling sharp edges to be defined. This can be useful in certain applications, such as defining borders or printing text comprising colored textures. 
   After compositing, the resultant image is dot formatted  662 , which includes ordering dots for output to the printhead and taking into account any spatial or operative compensation issues, as described in more detail below. The formatted dots are then supplied to the printhead for printing, again as described in more detail below. 
   In the second mode of operation, as shown in  FIG. 16 , the contone and bilevel components are received in uncompressed form by MoPEC directly into respective FIFOs  656  and  654 . The source of the components depends on the application. For example, the host processor in the mobile telecommunications device can be configured to generate the decompressed image components from compressed versions, or can simply be arranged to receive the uncompressed components from elsewhere, such as the mobile telecommunications network or the communication port described in more detail elsewhere. 
   Once the bilevel and contone components are in their respective FIFOs, MoPEC performs the same operations as described in relation to the first mode, and like numerals have therefore been used to indicate like functional blocks. 
   As shown in  FIG. 18 , the central data structure for the preferred printing architecture is a generalised representation of the three layers, called a page element. A page element can be used to represent units ranging from single rendered elements emerging from a rendering engine up to an entire page of a print job.  FIG. 18  shows a simplified UML diagram of a page element  300 . Conceptually, the bi-level symbol region selects between the two color sources. 
   MoPEC Device—Low level 
   The hardware components of a preferred MoPEC device  326  are shown in  FIG. 17  and described in more detail below. 
   Conceptually, a MoPEC device is simply a SoPEC device (ie, as described in cross-referenced application U.S. Ser. No. 10/727,181, filed on Dec. 2, 2003) that is optimized for use in a low-power, low print-speed environment of a mobile phone. Indeed, as long as power requirements are satisfied, a SoPEC device is capable of providing the functionality required of MoPEC. However, the limitations on battery power in a mobile device make it desirable to modify the SoPEC design. 
   As shown in  FIG. 17 , from the high level point of view a MoPEC consists of three distinct subsystems: a Central Processing Unit (CPU) subsystem  1301 , a Dynamic Random Access Memory (DRAM) subsystem  1302  and a Print Engine Pipeline (PEP) subsystem  1303 . 
   MoPEC has a much smaller eDRAM requirement than SoPEC. This is largely due to the considerably smaller print media for which MoPEC is designed to generate print data. 
   In one form, MoPEC can be provided in the form of a stand-alone ASIC designed to be installed in a mobile telecommunications device. Alternatively, it can be incorporated onto another ASIC that incorporates some or all of the other functionality required for the mobile telecommunications device. 
   The CPU subsystem  1301  includes a CPU that controls and configures all aspects of the other subsystems. It provides general support for interfacing and synchronizing the external printer with the internal print engine. It also controls low-speed communication to QA chips (which are described elsewhere in this specification) in cases where they are used. The preferred embodiment does not utilize QA chips in the cartridge or the mobile telecommunications device. 
   The CPU subsystem  1301  also contains various peripherals to aid the CPU, such as General Purpose Input Output (GPIO, which includes motor control), an Interrupt Controller Unit (ICU), LSS Master and general timers. The USB block provides an interface to the host processor in the mobile telecommunications device, as well as to external data sources where required. The selection of USB as a communication standard is a matter of design preference, and other types of communications protocols can be used, such as Firewire or SPI. 
   The DRAM subsystem  1302  accepts requests from the CPU, USB and blocks within the Print Engine Pipeline (PEP) subsystem. The DRAM subsystem  1302 , and in particular the DRAM Interface Unit (DIU), arbitrates the various requests and determines which request should win access to the DRAM. The DIU arbitrates based on configured parameters, to allow sufficient access to DRAM for all requestors. The DIU also hides the implementation specifics of the DRAM such as page size, number of banks and refresh rates. It will be appreciated that the DRAM can be considerably smaller than in the original SoPEC device, because the pages being printed are considerably smaller. Also, if the host processor can supply decompressed print data at a high enough rate, the DRAM can be made very small (of the order of 128-256 kbytes), since there is no need to buffer an entire page worth of information before commencing printing. 
   The Print Engine Pipeline (PEP) subsystem  1303  accepts compressed pages from DRAM and renders them to bi-level dots for a given print line destined for a printhead interface that communicates directly with the printhead. The first stage of the page expansion pipeline is the Contone Decoder Unit (CDU) and Lossless Bi-level Decoder (LBD). The CDU expands the JPEG-compressed contone (typically CMYK) layers and the LBD expands the compressed bi-level layer (typically K). The output from the first stage is a set of buffers: the Contone FIFO unit (CFU) and the Spot FIFO Unit (SFU). The CFU and SFU buffers are implemented in DRAM. 
   The second stage is the Halftone Compositor Unit (HCU), which halftones and dithers the contone layer and composites the bi-level spot layer over the resulting bi-level dithered layer. 
   A number of compositing options can be implemented, depending upon the printhead with which the MoPEC device is used. Up to six channels of bi-level data are produced from this stage, although not all channels may be present on the printhead. For example, in the preferred embodiment, the printhead is configured to print only CMY, with K pushed into the CMY channels, and IR omitted. 
   In the third stage, a Dead Nozzle Compensator (DNC) compensates for dead nozzles in the printhead by color redundancy and error diffusing of dead nozzle data into surrounding dots. 
   The resultant bi-level dot-data (being CMY in the preferred embodiment) is buffered and written to a set of line buffers stored in DRAM via a Dotline Writer Unit (DWU). 
   Finally, the dot-data is loaded back from DRAM, and passed to the printhead interface via a dot FIFO. The dot FIFO accepts data from a Line Loader Unit (LLU) at the system clock rate, while the PrintHead Interface (PHI) removes data from the FIFO and sends it to the printhead. 
   The amount of DRAM required will vary depending upon the particular implementation of MoPEC (including the system in which it is implemented). In this regard, the preferred MoPEC design is capable of being configured to operate in any of three modes. All of the modes available under the preferred embodiment assume that the received image data will be preprocessed in some way. The preprocessing includes, for example, color space conversion and scaling, where necessary. 
   In the first mode, the image data is decompressed by the host processor and supplied to MoPEC for transfer directly to the HCU. In this mode, the CDU and LBD are effectively bypassed, and the decompressed data is provided directly to the CFU and SFU to be passed on to the HCU. Because decompression is performed outside MoPEC, and the HCU and subsequent hardware blocks are optimized for their jobs, the MoPEC device can be clocked relatively slowly, and there is no need for the MoPEC CPU to be particularly powerful. As a guide, a clock speed of 10 to 20 MHz is suitable. 
   In the second mode, the image data is supplied to MoPEC in compressed form. To begin with, this requires an increase in MoPEC DRAM, to a minimum of about 256 kbytes (although double that is preferable). In the second mode, the CDU and LBD (and their respective buffers) are utilized to perform hardware decompression of the compressed contone and bilevel image data. Again, since these are hardware units optimized to perform their jobs, the system can be clocked relatively slowly, and there is still no need for a particularly powerful MoPEC processor. A disadvantage with this mode, however, is that the CDU and LBD, being hardware, are somewhat inflexible. They are optimized for particular decompression jobs, and in the preferred embodiment, cannot be reconfigured to any great extent to perform different decompression tasks. 
   In the third mode, the CDU and LBD are again bypassed, but MoPEC still receives image data in compressed form. Decompression is performed in software by the MoPEC CPU. Given that the CPU is a general-purpose processor, it must be relatively powerful to enable it to perform acceptably quick decompression of the compressed contone and bilevel image data. A higher clock speed will also be required, of the order of 3 to 10 times the clock speed where software decompression is not required. As with the second mode, at least 256 kbytes of DRAM are required on the MoPEC device. The third mode has the advantage of being programmable with respect to the type of decompression being performed. However, the need for a more powerful processor clocked at a higher speed means that power consumption will be correspondingly higher than for the first two modes. 
   It will be appreciated that enabling all of these modes to be selected in one MoPEC device requires the worst case features for all of the modes to be implemented. So, for example, at least 256 kbytes of DRAM, the capacity for higher clock speeds, a relatively powerful processor and the ability to selectively bypass the CDU and LBD must all be implemented in MoPEC. Of course, one or more of the modes can be omitted for any particular implementation, with a corresponding removal of the limitations of the features demanded by the availability of that mode. 
   In the preferred form, the MoPEC device is color space agnostic. Although it can accept contone data as CMYX or RGBX, where X is an optional 4th channel, it also can accept contone data in any print color space. Additionally, MoPEC provides a mechanism for arbitrary mapping of input channels to output channels, including combining dots for ink optimization and generation of channels based on any number of other channels. However, inputs are preferably CMY for contone input and K (pushed into CMY by MOPEC) for the bi-level input. 
   In the preferred form, the MoPEC device is also resolution agnostic. It merely provides a mapping between input resolutions and output resolutions by means of scale factors. The preferred resolution is 1600 dpi, but MoPEC actually has no knowledge of the physical resolution of the printhead to which it supplies dot data. 
                                           Unit               Subsystem   Acronym   Unit Name   Description                   DRAM   DIU   DRAM interface unit   Provides interface for DRAM read and write                   access for the various MoPEC units, CPU and                   the USB block. The DIU provides arbitration                   between competing units and controls DRAM                   access.           DRAM   Embedded DRAM   128 kbytes (or greater, depending upon                   implementation) of embedded DRAM.       CPU   CPU   Central Processing Unit   CPU for system configuration and                   control           MMU   Memory Management Unit   Limits access to certain memory address                   areas in CPU user mode           RDU   Real-time Debug Unit   Facilitates the observation of the                   contents of most of the CPU addressable                   registers in MoPEC, in addition to some                   pseudo-registers in real time           TIM   General Timer   ontains watchdog and general system                   timers           LSS   Low Speed Serial Interface   Low level controller for interfacing with                   QA chips           GPIO   General Purpose IOs   General IO controller, with built-in                   motor control unit, LED pulse units and                   de-glitch circuitry           ROM   Boot ROM   16 KBytes of System Boot ROM code           ICU   Interrupt Controller Unit   General Purpose interrupt controller with                   configurable priority, and masking.           CPR   Clock, Power and Reset block   Central Unit for controlling and                   generating the system clocks and resets                   and powerdown mechanisms           PSS   Power Save Storage   Storage retained while system is                   powered down           USB   Universal Serial Bus Device   USB device controller for interfacing                   with the host USB.       Print Engine   PCU   PEP controller   Provides external CPU with the means to       Pipeline           read and write PEP Unit registers, and read       (PEP)           and write DRAM in single 32-bit chunks.           CDU   Contone Decoder Unit   Expands JPEG compressed contone layer                   and writes decompressed contone to DRAM           CFU   Contone FIFO Unit   Provides line buffering between CDU and                   HCU           LBD   Lossless Bi-level Decoder   Expands compressed bi-level layer.           SFU   Spot FIFO Unit   Provides line buffering between LBD and                   HCU           HCU   Halftoner Compositor Unit   Dithers contone layer and composites the                   bi-level spot and position tag dots.           DNC   Dead Nozzle Compensator   Compensates for dead nozzles by color                   redundancy and error diffusing dead nozzle                   data into surrounding dots.           DWU   Dotline Writer Unit   Writes out dot data for a given printline to                   the line store DRAM           LLU   Line Loader Unit   Reads the expanded page image from line                   store, formatting the data appropriately for                   the bi-lithic printhead.           PHI   PrintHead Interface   Responsible for sending dot data to the                   printhead and for providing line                   synchronization between multiple MoPECs.                   Also provides test interface to printhead                   such as temperature monitoring and Dead                   Nozzle Identification.                    
Software Dot Generation
 
   Whilst speed and power consumption considerations make hardware acceleration desirable, it is also possible for some, most or all of the functions performed by the MoPEC integrated circuit to be performed by a general purpose processor programmed with suitable software routines. Whilst power consumption will typically increase to obtain similar performance with a general purpose processor (due to the higher overheads associated with having a general purpose processor perform highly specialized tasks such as decompression and compositing), this solution also has the advantage of easy customization and upgrading. For example, if a new or updated JPEG standard becomes widely used, it may be desirable to simply update the decompression algorithm performed by a general purpose processor. The decision to move some or all of the MoPEC integrated circuit&#39;s functionality into software needs to be made commercially on a case by case basis. 
   QA Chips 
   The preferred form of the invention does not use QA chips to authenticate the cartridge when it is inserted. However, in alternative embodiments, the print cartridge has a QA chip  82  that can be interrogated by a master QA chip  80  installed in the mobile device (see  FIG. 6 ). These are described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,164 until its serial number is assigned. In the interests of brevity, the disclosure of application Ser. No. 11/124,164 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Piezoelectric Drive System 
     FIGS. 19 to 22  show a piezoelectric drive system  126  for driving print media past the printhead. As best shown in  FIG. 21 , the drive system  126  includes a resonator  156  that includes a support end  158 , a through hole  160 , a cantilever  162  and a spring  164 . The support  158  is attached to the spring  164 , which in turn is attached to a mounting point  166  on the cradle  124 . A piezoelectric element  168  is disposed within the through hole  160 , extending across the hole to link the support end  158  with the cantilever  162 . The element  168  is positioned adjacent one end of the hole so that when it deforms, the cantilever  162  deflects from its quiescent position by a minute amount. 
   A tip  170  of the cantilever  162  is urged into contact with a rim of a drive wheel  172  at an angle of about 50 degrees. In turn, the drive wheel  172  engages a rubber roller  176  at the end of the drive shaft  178 . The drive shaft  178  engages and drives the print media past the printhead (described below with reference to  FIGS. 12 and 14 ). 
   Drive wires (not shown) are attached to opposite sides of the piezoelectric element  168  to enable supply of a drive signal. The spring, piezo and cantilever assembly is a structure with a set of resonant frequencies. A drive signal excites the structure to one of the resonant modes of vibration and causes the tip of the cantilever  162  to move in such a way that the drive wheel  172  rotates. In simple terms, when piezoelectric element expands, the tip  170  of the cantilever pushes into firmer contact with the rim of the drive wheel. Because the rim and the tip are relatively stiff, the moving tip causes slight rotation of the drive wheel in the direction shown. During the rest of the resonant oscillation, the tip  170  loses contact with the rim and withdraws slightly back towards the starting position. The subsequent oscillation then pushes the tip  170  down against the rim again, at a slightly different point, to push the wheel through another small rotation. The oscillatory motion of the tip  170  repeats in rapid succession and the drive wheel is moved in a series of small angular displacements. However, as the resonant frequency is high (of the order of kHz), the wheel  172 , for all intents and purposes, has a constant angular velocity. 
   In the embodiment shown, a drive signal at about 85 kHz rotates the drive wheel in the anti-clockwise direction (as shown in  FIG. 21 ). 
   Although the amount of movement per cycle is relatively small (of the order of a few micrometers), the high rate at which pulses are supplied means that a linear movement (i.e. movement of the rim) of up to 300 mm per second can be achieved. A different mode of oscillation can be caused by increasing the drive signal frequency to 95 kHz, which causes the drive wheel to rotate in the reverse direction. However, the preferred embodiment does not take advantage of the reversibility of the piezoelectric drive. 
   Precise details of the operation of the piezoelectric drive can be obtained from the manufacturer, Elliptec AG of Dortmund, Germany. 
   Other embodiments use various types of DC motor drive systems for feeding the media passed the printhead. These are described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,164. In the interests of brevity, the disclosure of application Ser. No. 11/124,164 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Print Cartridge 
   The print cartridge  148  is best shown in  FIGS. 23 and 24 , and takes the form of an elongate, generally rectangular box. The cartridge is based around a moulded housing  180  that includes three elongate slots  182 ,  184  and  186  configured to hold respective ink-bearing structures  188 ,  190 , and  192 . Each ink-bearing structure is typically a block of sponge-like material or laminated fibrous sheets. For example, these structures can be foam, a fibre and perforated membrane laminate, a foam and perforated membrane laminate, a folded perforated membrane, or sponge wrapped in perforated membrane. The ink bearing structures  188 ,  190  and  192  contain substantial void regions that contain ink, and are configured to prevent the ink moving around when the cartridge (or mobile telecommunications device in which it is installed) is shaken or otherwise moved. The amount of ink in each reservoir is not critical, but a typical volume per color would be of the order of 0.5 to 1.0 mL. 
   The porous material also has a capillary action that establishes a negative pressure at the in ejection nozzles (described in detail below). During periods of inactivity, the ink is retained in the nozzle chambers by the surface tension of the ink meniscus that forms across the nozzle. If the meniscus bulges outwardly, it can ‘pin’ itself to the nozzle rim to hold the ink in the chamber. However, if it contacts paper dust or other contaminants on the nozzle rim, the meniscus can be unpinned from the rim and ink will leak out of the printhead through the nozzle. 
   To address this, many ink cartridges are designed so that the hydrostatic pressure of the ink in the chambers is less than atmospheric pressure. This causes the meniscus at the nozzles to be concave or drawn inwards. This stops the meniscus from touching paper dust on the nozzle rim and removes the slightly positive pressure in the chamber that would drive the ink to leak out. 
   A housing lid  194  fits onto the top of the print cartridge to define ink reservoirs in conjunction with the ink slots  182 ,  184  and  186 . The lid can be glued, ultra-sonically welded, or otherwise form a seal with the upper edges of the ink slots to prevent the inks from moving between reservoirs or exiting the print cartridge. Ink holes  174  allow the reservoirs to be filled with ink during manufacture. Microchannel vents  140  define tortuous paths along the lid  196  between the ink holes  174  and the breather holes  154 . These vents allow pressure equalisation within the reservoirs when the cartridge  148  is in use while the tortuous path prevents ink leakage when the mobile phone  100  is moved through different orientations. A label  196  covers the vents  140 , and includes a tear-off portion  198  that is removed before use to expose breather holes  154  to vent the slots  182 ,  184  and  186  to atmosphere. 
   A series of outlets (not shown) in the bottom of each of the slots  182 ,  184  and  186 , lead to ink ducts  262  formed in the housing  180 . The ducts are covered by a flexible sealing film  264  that directs ink to a printhead IC  202 . One edge of the printhead IC  202  is bonded to the conductors on a flexible TAB film  200 . The bonds are covered and protected by an encapsulant strip  204 . Contacts  266  are formed on the TAB film  200  to enable power and data to be supplied to the printhead IC  202  via the conductors on the TAB film. The printhead IC  202  is mounted to the underside of the housing  180  by the polymer sealing film  264 . The film is laser drilled so that ink in the ducts  262  can flow to the printhead IC  202 . The sealing and ink delivery aspects of the film as discussed in greater detail below. 
   A capper  206  is attached to the chassis  180  by way of slots  208  that engage with corresponding moulded pins  210  on the housing. In its capped position, the capper  206  encloses and protects exposed ink in the nozzles (described below) of the printhead  202 . A pair of co-moulded elastomeric seals  240  on either side of the printhead IC  202  reduces its exposure to dust and air that can cause drying and clogging of the nozzles. 
   A metal cover  224  snaps into place during assembly to cover the capper  206  and hold it in position. The metal cover is generally U-shaped in cross section, and includes entry and exit slots  214  and  152  to allow media to enter and leave the print cartridge. Tongues  216  at either end of the metal cover  224  includes holes  218  that engages with complementary moulded pawls  220  in the lid  194 . A pair of capper leaf springs  238  are pressed from the bottom of the U-shape to bias the capper  206  against the printhead  202 . A tamper resistant label  222  is applied to prevent casual interference with the print cartridge  148 . 
   As discussed above, the media drive shaft  178  extends across the width of the housing  180  and is retained for rotation by corresponding holes  226  in the housing. The elastomeric drive wheel  176  is mounted to one end of the drive shaft  178  for engagement with the linear drive mechanism  126  when the print cartridge  148  is inserted into the mobile telecommunications device prior to use. 
   Alternative cartridge designs may have collapsible ink bags for inducing a negative ink pressure at the printhead nozzles. These and other alternatives, are described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,164. In the interests of brevity, the disclosure of application Ser. No. 11/124,164 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Printhead Mechanical 
   In the preferred form, a Memjet printer includes a monolithic pagewidth printhead. The printhead is a three-color 1600 dpi monolithic chip with an active print length of 2.165″ (55.0 mm). The printhead chip is about 800 microns wide and about 200 microns thick. 
   Power and ground are supplied to the printhead chip via two copper busbars approximately 200 microns thick, which are electrically connected to contact points along the chip with conductive adhesive. One end of the chip has several data pads that are wire bonded or ball bonded out to a small flex PCB and then encapsulated, as described in more detail elsewhere. 
   In alterative embodiments, the printhead can be constructed using two or more printhead chips, as described in relation to the SoPEC-based bilithic printhead arrangement described in U.S. Ser. No. 10/754,536 filed on Jan. 12, 2004, the contents of which are incorporated herein by cross-reference. In yet other embodiments, the printhead can be formed from one or more monolithic printheads comprising linking printhead modules as described in U.S. Ser. No. 10/754,536 filed on Jan. 12, 2004, the contents of which are incorporated herein by cross-reference. 
   In the preferred form, the printhead is designed to at least partially self-destruct in some way to prevent unauthorized refilling with ink that might be of questionable quality. Self-destruction can be performed in any suitable way, but the preferred mechanism is to include at least one fusible link within the printhead that is selectively blown when it is determined that the ink has been consumed or a predetermined number of prints has been performed. 
   Alternatively or additionally, the printhead can be designed to enable at least partial re-use of some or all of its components as part of a remanufacturing process. 
   Fusible links on the printhead integrated circuit (or on a separate integrated circuit in the cartridge) can also be used to store other information that the manufacturer would prefer not to be modified by end-users. A good example of such information is ink-remaining data. By tracking ink usage and selectively blowing fusible links, the cartridge can maintain an unalterable record of ink usage. For example, ten fusible links can be provided, with one of the fusible links being blown each time it is determined that a further 10% of the total remaining ink has been used. A set of links can be provided for each ink or for the inks in aggregate. Alternatively or additionally, a fusible link can be blown in response to a predetermined number of prints being performed. 
   Fusible links can also be provided in the cartridge and selectively blown during or after manufacture of the cartridge to encode an identifier (unique, relatively unique, or otherwise) in the cartridge. 
   The fusible links can be associated with one or more shift register elements in the same way as data is loaded for printing (as described in more detail below). Indeed, the required shift register elements can form part of the same chain of register elements that are loaded with dot data for printing. In this way, the MoPEC chip is able to control blowing of fusible links simply by changing data that is inserted into the stream of data loaded during printing. Alternatively or additionally, the data for blowing one or more fusible links can be loaded during a separate operation to dot-data loading (ie, dot data is loaded as all zeros). Yet another alternative is for the fusible links to be provided with their own shift register which is loaded independently of the dot data shift register. 
     FIGS. 25 and 26  show basic circuit diagrams of a 10-fuse link and a single fuse cell respectively.  FIG. 25  shows a shift register  373  that can be loaded with values to be programmed into the 1-bit fuse cells  375 ,  377  and  379 . Each shift register latch  381 ,  383  and  385  connects to a 1-bit fuse cell respectively, providing the program value to its corresponding cell. The fuses are programmed by setting the fuse_program_enable signal  387  to 1. The fuse cell values  391 ,  393  and  395  are loaded into a 10-bit register  389 . This value  389  can be accessed by the printhead IC control logic, for example to inhibit printing when the fuse value is all ones. Alternatively or additionally, the value  397  can be read serially by MoPEC, to see the state of the fuses  375 ,  377  and  379  after MoPEC is powered up. 
   A possible fuse cell  375  is shown in  FIG. 26 . Before being blown, the fuse element structure itself has a electrical resistance  405 , which is substantially lower than the value of the pullup resistor  407 . This pulls down the node A, which is buffered to provide the fuse_value output  391 , initially a zero. A fuse is blown when fuse_program_enable  387  and fuse_program_value  399  are both 1. This causes the PFET  409  connecting node A to Vpos is turn on, and current flows that causes the fuse element to go open circuit, i.e. resistor  405  becomes infinite. Now the fuse_value output  391  will read back as a one. 
   Sealing The Printhead 
   As briefly mentioned above, the printhead IC  202  is mounted to the underside of the housing  180  by the polymer sealing film  264  (see  FIG. 24 ). This film may be a thermoplastic film such as a PET or Polysulphone film, or it may be in the form of a thermoset film, such as those manufactured by AL technologies and Rogers Corporation. The polymer sealing film  264  is a laminate with adhesive layers on both sides of a central film, and laminated onto the underside of the moulded housing  180 . A plurality of holes (not shown) are laser drilled through the sealing film  264  to coincide with ink delivery points in the ink ducts  262  (or in the case of the alternative cartridge, the ink ducts  320  in the film layer  318 ) so that the printhead IC  202  is in fluid communication with the ink ducts  262  and therefore the ink retaining structures  188 ,  190  and  192 . 
   The thickness of the polymer sealing film  264  is critical to the effectiveness of the ink seal it provides. The film seals the ink ducts  262  on the housing  180  (or the ink ducts  320  in the film layer  318 ) as well as the ink conduits (not shown) on the reverse side of the printhead IC  202 . However, as the film  264  seals across the ducts  262 , it can also bulge into one of conduits on the reverse side of the printhead IC  202 . The section of film bulging into the conduit, may run across several of the ink ducts  262  in the printhead IC  202 . The sagging may cause a gap that breaches the seal and allows ink to leak from the printhead IC  202  and or between the conduits on its reverse side. 
   To guard against this, the polymer sealing film  264  should be thick enough to account for any bulging into the ink ducts  262  (or the ink ducts  320  in the film layer  318 ) while maintaining the seal on the back of the printhead IC  202 . The minimum thickness of the polymer sealing film  264  will depend on:
         the width of the conduit into which it sags;   the thickness of the adhesive layers in the film&#39;s laminate structure;   the ‘stiffness’ of the adhesive layer as the printhead IC  202  is being pushed into it; and,   the modulus of the central film material of the laminate.       

   A polymer sealing film  264  thickness of 25 microns is adequate for the printhead IC and cartridge assembly shown. However, increasing the thickness to 50, 100 or even 200 microns will correspondingly increase the reliability of the seal provided. 
   Printhead CMOS 
   Turning now to  FIGS. 27 to 46 , a preferred embodiment of the printhead  420  (comprising printhead IC  425 ) will be described. 
     FIG. 27  shows an overview of printhead IC  425  and its connections to the MoPEC device  166 . Printhead IC  425  includes a nozzle core array  401  containing the repeated logic to fire each nozzle, and nozzle control logic  402  to generate the timing signals to fire the nozzles. The nozzle control logic  402  receives data from the MoPEC chip  166  via a high-speed link. In the preferred form, a single MoPEC chip  166  feeds the two printhead ICs  425  and  426  with print data. 
   The nozzle control logic is configured to send serial data to the nozzle array core for printing, via a link  407 , which for printhead  425  is the electrical connector  428 . Status and other operational information about the nozzle array core  401  is communicated back to the nozzle control logic via another link  408 , which is also provided on the electrical connector  428 . 
   The nozzle array core  401  is shown in more detail in  FIGS. 28 and 29 . In  FIG. 28 , it will be seen that the nozzle array core comprises an array of nozzle columns  501 . The array includes a fire/select shift register  502  and three color channels, each of which is represented by a corresponding dot shift register  503 . 
   As shown in  FIG. 29 , the fire/select shift register  502  includes a forward path fire shift register  600 , a reverse path fire shift register  601  and a select shift register  602 . Each dot shift register  503  includes an odd dot shift register  603  and an even dot shift register  604 . The odd and even dot shift registers  603  and  604  are connected at one end such that data is clocked through the odd shift register  603  in one direction, then through the even shift register  604  in the reverse direction. The output of all but the final even dot shift register is fed to one input of a multiplexer  605 . This input of the multiplexer is selected by a signal (corescan) during post-production testing. In normal operation, the corescan signal selects dot data input Dot[x] supplied to the other input of the multiplexer  605 . This causes Dot[x] for each color to be supplied to the respective dot shift registers  503 . 
   A single column N will now be described with reference to  FIG. 29 . In the embodiment shown, the column N includes six data values, comprising an odd data value held by an element  606  of the odd shift register  603 , and an even data value held by an element  607  of the even shift register  604 , for each of the three dot shift registers  503 . Column N also includes an odd fire value  608  from the forward fire shift register  600  and an even fire value  609  from the reverse fire shift register  601 , which are supplied as inputs to a multiplexer  610 . The output of the multiplexer  610  is controlled by the select value  611  in the select shift register  602 . When the select value is zero, the odd fire value is output, and when the select value is one, the even fire value is output. 
   The values from the shift register elements  606  and  607  are provided as inputs to respective odd and even dot latches  612  and  613  respectively. 
   Each of dot latch  612  and  613  and their respective associated shift register elements form a unit cell  614 , which is shown in more detail in  FIG. 30 . The dot latch  612  is a D-type flip-flop that accepts the output of the shift register element  606 . The data input d to the shift register element  606  is provided from the output of a previous element in the odd dot shift register (unless the element under consideration is the first element in the shift register, in which case its input is the Dot[x] value). Data is clocked from the output of flip-flop  606  into latch  612  upon receipt of a negative pulse provided on LsyncL. 
   The output of latch  612  is provided as one of the inputs to a three-input AND gate  65 . Other inputs to the AND gate  615  are the Fr signal (from the output of multiplexer  610 ) and a pulse profile signal Pr. The firing time of a nozzle is controlled by the pulse profile signal Pr, and can be, for example, lengthened to take into account a low voltage condition that arises due to low battery (in a battery-powered embodiment). This is to ensure that a relatively consistent amount of ink is efficiently ejected from each nozzle as it is fired. In the embodiment described, the profile signal Pr is the same for each dot shift register, which provides a balance between complexity, cost and performance. However, in other embodiments, the Pr signal can be applied globally (ie, is the same for all nozzles), or can be individually tailored to each unit cell or even to each nozzle. 
   Once the data is loaded into the latch  612 , the fire enable Fr and pulse profile Pr signals are applied to the AND gate  615 , combining to the trigger the nozzle to eject a dot of ink for each latch  612  that contains a logic 1. 
   The signals for each nozzle channel are summarized in the following table: 
   
     
       
             
             
             
           
         
             
                 
             
             
               Name 
               Direction 
               Description 
             
             
                 
             
           
           
             
               d 
               Input 
               Input dot pattern to shift register bit 
             
             
               q 
               Output 
               Output dot pattern from shift register bit 
             
             
               SrClk 
               Input 
               Shift register clock in - d is captured on rising 
             
             
                 
                 
               edge of this clock 
             
             
               LsyncL 
               Input 
               Fire enable - needs to be asserted for nozzle to fire 
             
             
               Pr 
               Input 
               Profile - needs to be asserted for nozzle to fire 
             
             
                 
             
           
        
       
     
   
   As shown in  FIG. 30 , the fire signals Fr are routed on a diagonal, to enable firing of one color in the current column, the next color in the following column, and so on. This averages the current demand by spreading it over the three nozzle columns in time-delayed fashion. 
   The dot latches and the latches forming the various shift registers are fully static in this embodiment, and are CMOS-based. The design and construction of latches is well known to those skilled in the art of integrated circuit engineering and design, and so will not be described in detail in this document. 
   The combined printhead ICs define a printhead having 13824 nozzles per color. The circuitry supporting each nozzle is the same, but the pairing of nozzles happens due to physical positioning of the MEMS nozzles; odd and even nozzles are not actually on the same horizontal line, as shown in  FIG. 31 . 
   Nozzle Design—Thermal Actuator 
   An alternative nozzle design utilises a thermal inkjet mechanism for expelling ink from each nozzle. The thermal nozzles are set out similarly to their mechanical equivalents, and are supplied by similar control signals by similar CMOS circuitry, albeit with different pulse profiles if required by any differences in drive characteristics need to be accounted for. 
   With reference to  FIGS. 32 to 36 , the nozzle of a printhead according to an embodiment of the invention comprises a nozzle plate  902  with nozzles  903  therein, the nozzles having nozzle rims  904 , and apertures  905  extending through the nozzle plate. The nozzle plate  902  is plasma etched from a silicon nitride structure which is deposited, by way of chemical vapor deposition (CVD), over a sacrificial material which is subsequently etched. 
   The printhead also includes, with respect to each nozzle  903 , side walls  906  on which the nozzle plate is supported, a chamber  907  defined by the walls and the nozzle plate  902 , a multi-layer substrate  908  and an inlet passage  909  extending through the multi-layer substrate to the far side (not shown) of the substrate. A looped, elongate heater element  910  is suspended within the chamber  907 , so that the element is in the form of a suspended beam. The printhead as shown is a microelectromechanical system (MEMS) structure, which is formed by a lithographic process which is described in more detail below. 
   When the printhead is in use, ink  911  from a reservoir (not shown) enters the chamber  907  via the inlet passage  909 , so that the chamber fills to the level as shown in  FIG. 32 . Thereafter, the heater element  910  is heated for somewhat less than 1 micro second, so that the heating is in the form of a thermal pulse. It will be appreciated that the heater element  910  is in thermal contact with the ink  911  in the chamber  907  so that when the element is heated, this causes the generation of vapor bubbles  912  in the ink. Accordingly, the ink  911  constitutes a bubble forming liquid.  FIG. 32  shows the formation of a bubble  912  approximately 1 microsecond after generation of the thermal pulse, that is, when the bubble has just nucleated on the heater elements  910 . It will be appreciated that, as the heat is applied in the form of a pulse, all the energy necessary to generate the bubble  12  is to be supplied within that short time. 
   In operation, voltage is applied across electrodes (not shown) to cause current to flow through the elements  910 . The electrodes  915  are much thicker than the element  910  so that most of the electrical resistance is provided by the element. Thus, nearly all of the power consumed in operating the heater  914  is dissipated via the element  910 , in creating the thermal pulse referred to above. 
   When the element  910  is heated as described above, the bubble  912  forms along the length of the element, this bubble appearing, in the cross-sectional view of  FIG. 32 , as four bubble portions, one for each of the element portions shown in cross section. 
   The bubble  912 , once generated, causes an increase in pressure within the chamber  97 , which in turn causes the ejection of a drop  916  of the ink  911  through the nozzle  903 . The rim  904  assists in directing the drop  916  as it is ejected, so as to minimize the chance of drop misdirection. 
   The reason that there is only one nozzle  903  and chamber  907  per inlet passage  909  is so that the pressure wave generated within the chamber, on heating of the element  910  and forming of a bubble  912 , does not affect adjacent chambers and their corresponding nozzles. 
   The advantages of the heater element  910  being suspended rather than being embedded in any solid material, is discussed below. 
     FIGS. 33 and 34  show the unit cell  901  at two successive later stages of operation of the printhead. It can be seen that the bubble  912  generates further, and hence grows, with the resultant advancement of ink  911  through the nozzle  903 . The shape of the bubble  912  as it grows, as shown in  FIG. 34 , is determined by a combination of the inertial dynamics and the surface tension of the ink  911 . The surface tension tends to minimize the surface area of the bubble  912  so that, by the time a certain amount of liquid has evaporated, the bubble is essentially disk-shaped. 
   The increase in pressure within the chamber  907  not only pushes ink  911  out through the nozzle  903 , but also pushes some ink back through the inlet passage  909 . However, the inlet passage  909  is approximately 200 to 300 microns in length, and is only approximately 16 microns in diameter. Hence there is a substantial viscous drag. As a result, the predominant effect of the pressure rise in the chamber  907  is to force ink out through the nozzle  903  as an ejected drop  916 , rather than back through the inlet passage  909 . 
   Turning now to  FIG. 35 , the printhead is shown at a still further successive stage of operation, in which the ink drop  916  that is being ejected is shown during its “necking phase” before the drop breaks off. At this stage, the bubble  912  has already reached its maximum size and has then begun to collapse towards the point of collapse  917 , as reflected in more detail in  FIG. 36 . 
   The collapsing of the bubble  912  towards the point of collapse  917  causes some ink  911  to be drawn from within the nozzle  903  (from the sides  918  of the drop), and some to be drawn from the inlet passage  909 , towards the point of collapse. Most of the ink  911  drawn in this manner is drawn from the nozzle  903 , forming an annular neck  919  at the base of the drop  916  prior to its breaking off. 
   The drop  916  requires a certain amount of momentum to overcome surface tension forces, in order to break off. As ink  911  is drawn from the nozzle  903  by the collapse of the bubble  912 , the diameter of the neck  919  reduces thereby reducing the amount of total surface tension holding the drop, so that the momentum of the drop as it is ejected out of the nozzle is sufficient to allow the drop to break off. 
   When the drop  916  breaks off, cavitation forces are caused as reflected by the arrows  920 , as the bubble  912  collapses to the point of collapse  917 . It will be noted that there are no solid surfaces in the vicinity of the point of collapse  917  on which the cavitation can have an effect. 
   The nozzles may also use a bend actuated arm to eject ink drops. These so called ‘thermal bend’ nozzles are set out similarly to their bubble forming thermal element equivalents, and are supplied by similar control signals by similar CMOS circuitry, albeit with different pulse profiles if required by any differences in drive characteristics need to be accounted for. A thermal bend nozzle design is described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,164. In the interests of brevity, the disclosure of application Ser. No. 11/124,177 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Cradle 
   The various cartridges described above are used in the same way, since the mobile device itself cannot tell which ink supply system is in use. Hence, the cradle will be described with reference to the cartridge  148  only. 
   Referring to  FIG. 37 , the cartridge  148  is inserted axially into the mobile phone  100  via the access cover  282  and into engagement with the cradle  124 . As previously shown in  FIGS. 19 and 21 , the cradle  124  is an elongate U-shaped moulding defining a channel that is dimensioned to closely correspond to the dimensions of the print cartridge  148 . Referring now to  FIG. 38 , the cartridge  148  slides along the rail  328  upon insertion into the mobile phone  100 . The edge of the lid moulding  194  fits under the rail  328  for positional tolerance control. As shown in  FIGS. 19 to 21  the contacts  266  on the cartridge TAB film  200  are urged against the data/power connector  330  in the cradle. The other side of the data/power connector  330  contacts the cradle flex PCB  332 . This PCB connects the cartridge and the MoPEC chip to the power and the host electronics (not shown) of the mobile phone, to provide power and dot data to the printhead to enable it to print. The interaction between the MoPEC chip and the host electronics of the mobile telecommunications device is described in the Netpage and Mobile Telecommunications Device Overview section above. 
   Media Feed 
     FIGS. 12 to 14  show the medium being fed through the mobile telecommunications device and printed by the printhead.  FIG. 12  shows the blank medium  226 , in this case a card, being fed into the left side of the mobile phone  100 .  FIG. 13  is section view taken along A-A of  FIG. 12 . It shows the card  226  entering the mobile telecommunications device through a card insertion slot  228  and into the media feed path leading to the print cartridge  148  and print cradle  124 . The rear cover moulding  106  has guide ribs that taper the width of the media feed path into a duct slightly thicker than the card  226 . In  FIG. 13  the card  226  has not yet entered the print cartridge  148  through the slot  214  in the metal cover  224 . The metal cover  224  has a series of spring fingers  230  (described in more detail below) formed along one edge of the entry slot  214 . These fingers  230  are biased against the drive shaft  178  so that when the card  226  enters the slot  214 , as shown in  FIG. 14 , the fingers guide it to the drive shaft  178 . The nip between the drive shaft  178  and the fingers  230  engages the card  226  and it is quickly drawn between them. The fingers  230  press the card  226  against the drive shaft  178  to drive it past the printhead  202  by friction. The drive shaft  178  has a rubber coating to enhance its grip on the medium  226 . Media feed during printing is described in a later section. 
   It is preferred that the drive mechanism be selected to print the print medium in about 2 to 4 seconds. Faster speeds require relatively higher drive currents and impose restrictions on peak battery output, whilst slower speeds may be unacceptable to consumers. However, faster or slower speeds can certainly be catered for where there is commercial demand. 
   Decapping 
   The decapping of the printhead  202  is shown in  FIGS. 39 to 48 .  FIG. 39  shows print cartridge  148  immediately before the card  226  is fed into the entry slot  214 . The capper  206  is biased into the capped position by the capper leaf springs  238 . The capper&#39;s elastomeric seal  240  protects the printhead from paper dust and other contaminants while also stopping the ink in the nozzles from drying out when the printhead is not in use. 
   Referring to  FIGS. 39 and 42 , the card  226  has been fed into the print cartridge  148  via the entry slot  214 . The spring fingers  230  urge the card against the drive shaft  178  as it driven past the printhead. Immediately downstream of the drive shaft  178 , the leading edge of the card  226  engages the inclined front surface of the capper  206  and pushes it to the uncapped position against the bias of the capper leaf springs  238 . The movement of the capper is initially rotational, as the linear movement of the card causes the capper  206  to rotate about the pins  210  that sit in its slots  208  (see  FIG. 24 ). However, as shown in  FIGS. 43 to 45 , the capper is constrained such that further movement of the card begins to cause linear movement of the capper directly down and away from the printhead chip  202 , against the biasing action of spring  238 . Ejection of ink from the printhead IC  202  onto the card commences as the leading edge of the card reaches the printhead. 
   As best shown in  FIG. 45 , the card  226  continues along the media path until it engages the capper lock actuating arms  232 . This actuates the capper lock to hold the capper in the uncapped position until printing is complete. This is described in greater detail below. 
   Capping 
   As shown in  FIGS. 46 to 48 , the capper remains in the uncapped position until the card  226  disengages from the actuation arms  232 . At this point the capper  206  is unlocked and returns to its capped position by the leaf spring  230 . 
   Capper Locking and Unlocking 
   Referring to  FIGS. 49 to 53 , the card  226  slides over the elastomeric seal  240  as it is driven past the printhead  202 . The leading edge of the card  226  then engages the pair of capper locking mechanisms  212  at either side of the media feed path. The capper locking mechanisms  212  are rotated by the card  226  so that its latch surfaces  234  engage lock engagement faces  236  of the capper  206  to hold it in the uncapped position until the card is removed from the print cartridge  148 . 
     FIGS. 49 and 52  show the locking mechanisms  212  in their unlocked condition and the capper  206  in the capped position. The actuation arms  232  of each capper lock mechanism  212  protrude into the media path. The sides of the capper  206  prevent the actuation arms from rotating out of the media feed path. Referring to  FIGS. 50 ,  51 A,  51 B and  53 , the leading edge of the card  226  engages the arms  232  of the capper lock mechanisms  212  protruding into the media path from either side. When the leading edge has reached the actuation arms  232 , the card  226  has already pushed the capper  206  to the uncapped position so the locking mechanisms  212  are now free to rotate. As the card pushes past the arms  232 , the lock mechanisms  212  rotate such that their respective chamfered latch surfaces  234  slidingly engage the angled lock engagement face  238  on either side of the capper  206 . The sliding engagement of between these faces pushes the capper  206  clear of the card  226  so that it no longer touches the elastomeric seals  240 . This reduces the drag retarding the media feed. The sides of the card  226  sliding against the actuation arms  232  prevent the locking mechanisms  212  from rotating so the capper  206  is locked in the uncapped position by the latch surfaces  234  pressing against the lock engagement face  238 . 
   When the printed card  226  is retrieved by the user (described in more detail below), the actuation arms  232  are released and free to rotate. The capper leaf springs  238  return the capper  206  to the capped position, and in so doing, the latch surfaces  234  slide over the lock engagement faces  236  so that the actuation arms  232  rotate back out into the media feed path. 
   Alternative capping mechanisms are possible and a selection of these have been described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,167. In the interests of brevity, the disclosure of application Ser. No. 11/124,167 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Print Media and Printing 
   A Netpage printer normally prints the tags which make up the surface coding on demand, i.e. at the same time as it prints graphic page content. As an alternative, in a Netpage printer not capable of printing tags such as the preferred embodiment, pre-tagged but otherwise blank Netpages can be used. The printer, instead of being capable of tag printing, typically incorporates a Netpage tag sensor. The printer senses the tags and hence the region ID of a blank either prior to, during, or after the printing of the graphic page content onto the blank. It communicates the region ID to the Netpage server, and the server associates the page content and the region ID in the usual way. 
   A particular Netpage surface coding scheme allocates a minimum number of bits to the representation of spatial coordinates within a surface region. If a particular media size is significantly smaller than the maximum size representable in the minimum number of bits, then the Netpage code space may be inefficiently utilised. It can therefore be of interest to allocate different sub-areas of a region to a collection of blanks. Although this makes the associations maintained by the Netpage server more complex, and makes subsequent routing of interactions more complex, it leads to more efficient code space utilisation. In the limit case the surface coding may utilise a single region with a single coordinate space, i.e. without explicit region IDs. 
   If regions are sub-divided in this way, then the Netpage printer uses the tag sensor to determine not only the region ID but also the surface coding location of a known physical position on the print medium, i.e. relative to two edges of the medium. From the surface coding location and its corresponding physical position on the medium, and the known (or determined) size of the medium, it then determines the spatial extent of the medium in the region&#39;s coordinate space, and communicates both the region ID and the spatial extent to the server. The server associates the page content with the specified sub-area of the region. 
   A number of mechanisms can be used to read tag data from a blank. A conventional Netpage tag sensor incorporating a two-dimensional image sensor can be used to capture an image of the tagged surface of the blank at any convenient point in the printer&#39;s paper path. As an alternative, a linear image sensor can be used to capture successive line images of the tagged surface of the blank during transport. The line images can be used to create a two-dimensional image which is processed in the usual way. As a further alternative, region ID data and other salient data can be encoded linearly on the blank, and a simple photodetector and ADC can be used to acquire samples of the linear encoding during transport. 
   One important advantage of using a two-dimensional image sensor is that tag sensing can occur before motorised transport of the print medium commences. I.e. if the print medium is manually inserted by the user, then tag sensing can occur during insertion. This has the further advantage that if the tag data is validated by the device, then the print medium can be rejected and possibly ejected before printing commences. For example, the print medium may have been pre-printed with advertising or other graphic content on the reverse side from the intended printing side. The device can use the tag data to detect incorrect media insertion, i.e. upside-down or back-to-front. The device can also prevent accidental overprinting of an already-printed medium. And it can detect the attempted use of an invalid print medium and refuse printing, e.g. to protect print quality. The device can also derive print medium characteristics from the tag data, to allow it to perform optimal print preparation. 
   If a linear image sensor is used, or if a photodetector is used, then image sensing must occur during motorised transport of the print medium to ensure accurate imaging. Unless there are at least two points of contact between the transport mechanism and the print medium in the printing path, separated by a minimum distance equal to the tag data acquisition distance, tag data cannot be extracted before printing commences, and the validation advantages discussed above do not obtain. In the case of a linear image sensor, the tag data acquisition distance equals the diameter of the normal tag imaging field of view. In the case of a photodetector, the tag data acquisition distance is as long as the required linear encoding. 
   If the tag sensor is operable during the entire printing phase at a sufficiently high sampling rate, then it can also be used to perform accurate motion sensing, with the motion data being used to provide a line synchronisation signal to the print engine. This can be used to eliminate the effects of jitter in the transport mechanism. 
     FIGS. 54 to 60  show one embodiment of the encoded medium and the media sensing and printing system within the mobile telecommunications device. While the encoding of the cards is briefly discussed here, it is described in detail in the Coded Media sub-section of this specification. Likewise, the optical sensing of the encoded data is described elsewhere in the specification and a comprehensive understanding of the M-Print media and printing system requires the specification to be read in its entirety. 
   Referring to  FIG. 54 , the ‘back-side’ of one of the cards  226  is shown. The back-side of the card has two coded data tracks: a ‘clock track’  434  and a ‘data track’  436  running along the longitudinal sides of the cards. The cards are encoded with data indicating, inter alia:
         the orientation of the card;   the media type and authenticity;   the longitudinal size;   the pre-printed side;   detection of prior printing on the card; and,   the position of the card relative to the printhead IC.       

   Ideally, the encoded data is printed in IR ink so that it is invisible and does not encroach on the space available for printing visible images. 
   In a basic form, the M-Print cards  226  are only encoded with a data track and clocking (as a separate clock track or a self-clocking data track). However, in the more sophisticated embodiment shown in the figures, the cards  226  have a pre-printed Netpage tag pattern  438  covering the majority of the back-side. The front side may also have a pre-printed tag pattern. In these embodiments, it is preferable that the data track encodes first information that is at least indicative of second information encoded in the tags. Most preferably, the first information is simply the document identity that is encoded in each of the tags. 
   The clock track  434  allows the MoPEC  326  (see  FIG. 55 ) to determine, by its presence, that the front of the card  226  is facing the printhead  202 , and allows the printer to sense the motion of the card  226  during printing. The clock track  434  also provides a clock for the densely coded data track  436 . 
   The data track  436  provides the Netpage identifier and optionally associated digital signatures (as described elsewhere in the specification) which allows MoPEC  326  to reject fraudulent or un-authorised media  226 , and to report the Netpage identifier of the front-side Netpage tag pattern to a Netpage server. 
     FIG. 55  shows a block diagram of an M-Print system that uses media encoded with separate clock and data tracks. The clock and data tracks are read by separate optical encoders. The system may optionally have an explicit edge detector  474  which is discussed in more detail below in relation to  FIG. 58 . 
     FIG. 56  shows a simplified circuit for an optical encoder which may be used as the clock track or data track optical encoder. It incorporates a Schmitt trigger  466  to provide the MoPEC  326  with an essentially binary signal representative of the marks and spaces encountered by the encoder in the clock or data track. An IR LED  472  is configured to illuminate a mark-sized area of the card  226  and a phototransistor  468  is configured to capture the light  470  reflected by the card. The LED  472  has a peak wavelength matched to the peak absorption wavelength of the infrared ink used to print the media coding. 
   As an alternative, the optical encoders can sense the direction of media movement by configuring them to be ‘quadrature encoders’. A quadrature encoder contains a pair of optical encoders spatially positioned to read the clock track 90 degrees out of phase. Its in-phase and quadrature outputs allow the MoPEC  326  to identify not just the motion of the clock track  434  but also the direction of the motion. A quadrature encoder is generally not required, since the media transport direction is known a priori because the printer controller also controls the transport motor. However, the use of a quadrature encoder can help decouple a bi-directional motion sensing mechanism from the motion control mechanism. 
     FIG. 57  shows a block diagram of the MoPEC  326 . It incorporates a digital phase lock loop (DPLL)  444  to track the clock inherent in the clock track  434  (see  FIG. 54 ), a line sync generator  448  to generate the line sync signal  476  from the clock  446 , and a data decoder  450  to decode the data in the data track  436 . De-framing, error detection and error correction may be performed by software running on MoPEC&#39;s general-purpose processor  452 , or it may be performed by dedicated hardware in MoPEC. 
   The data decoder  450  uses the clock  446  recovered by the DPLL  444  to sample the signal from the data track optical encoder  442 . It may either sample the continuous signal from the data track optical encoder  442 , or it may actually trigger the LED of the data track optical encoder  442  for the duration of the sample period, thereby reducing the total power consumption of the LED. 
   The DPLL  444  may be a PLL, or it may simply measure and filter the period between successive clock pulses. 
   The line sync generator  456  consists of a numerically-controlled oscillator which generates line sync pulses  476  at a rate which is a multiple of the rate of the clock  446  recovered from the clock track  434 . 
   As shown in  FIG. 55 , the print engine may optionally incorporate an explicit edge detector  474  to provide longitudinal registration of the card  226  with the operation of the printhead  202 . In this case, as shown in  FIG. 58 , it generates a page sync signal  478  to signal the start of printing after counting a fixed number of line syncs  476  after edge detection. Longitudinal registration may also be achieved by other card-in detection mechanisms ranging from opto-sensors, de-capping mechanical switches, drive shaft/tension spring contact switch and motor load detection. 
   Optionally, the printer can rely on the media coding itself to obtain longitudinal registration. For example, it may rely on acquisition of a pilot sequence on the data track  436  to obtain registration. In this case, as shown in  FIG. 59 , it generates a page sync signal  478  to signal the start of printing after counting a fixed number of line syncs  476  after pilot detection. The pilot detector  460  consists of a shift register and combinatorial logic to recognise the pilot sequence  480  provided by the data decoder  450 , and generate the pilot sync signal  482 . Relying on the media coding itself can provide superior information for registering printed content with the Netpage tag pattern  438  (see  FIG. 54 ). 
   As shown in  FIG. 60 , the data track optical encoder  442  is positioned adjacent to the first clock data encoder  440 , so that the data track  436  (see  FIG. 54 ) can be decoded as early as possible and using the recovered clock signal  446 . The clock must be acquired before printing can commence, so a first optical encoder  440  is positioned before the printhead  202  in the media feed path. However, as the clock needs to be tracked throughout the print, a second clock optical encoder  464  is positioned coincident with or downstream of the printhead  202 . This is described in more detail below. 
     FIG. 47  shows the printed card  226  being withdrawn from the print cartridge  148 . It will be appreciated that the printed card  226  needs to be manually withdrawn by the user. Once the trailing edge of the card  226  has passed between the drive shaft  178  and the spring fingers  238 , it is no longer driven along the media feed path. However, as the printhead  202  is less than 2 mm from the drive shaft  178 , the momentum of the card  226  projects the trailing edge of past the printhead  202 . 
   While the momentum of the card is sufficient to carry the trailing edge past the printhead, it is not enough to fling it out of the exit slot  150  ( FIG. 14 ). Instead, the card  226  is lightly gripped by the opposed lock actuator arms  232  as it protrudes from the exit slot  150  in the side of the mobile phone  100 . This retains the card  226  so it does not simply fall from exit slot  150 , but rather allows users to manually remove the printed card  226  from the mobile phone  100  at their convenience. This is important to the practicality of the mobile telecommunications device because the card  226  is fed into one side of the mobile telecommunications device and retrieved from the other, so users will typically want to swap the hand that holds the mobile telecommunications device when collecting the printed card. By lightly retaining the printed card, users do not need to swap hands and be ready to collect the card before completion of the print job (approximately 1-2 secs). 
   Alternatively, the velocity of the card as it leaves the roller can be made high enough that the card exits the outlet slot  123  under its own inertia. 
   Dual Clock Sensor Synchronization 
   For full bleed printing, the decoder needs to generate a line sync signal for the entire longitudinal length of the card. Unless the card has a detachable strip (described elsewhere in the specification), the print engine will need two clock track sensors; one either side of printhead. Initially the line sync signal is generated from the clock signal from the pre-printhead sensor and then, before the trailing edge of the card passes the pre-printhead sensor, the line sync signal needs to be generated by the post-printhead sensor. In order to switch from the first clock signal to the second, the second needs to be synchronized with the first to avoid any discontinuity in the line sync signal (which cause artefacts in the print). 
   Referring to  FIG. 62 , a pair of DPLL&#39;s  443  and  444  track the clock inherent in the clock track, via respective first and second clock track optical encoders  440  and  464 . During the initial phase of the print only the first encoder  440  will be seeing the clock track and only the first PLL  443  will be locked. The card is printed as it passes the printhead and then the second clock track optical encoder  464  sees the clock track. At this stage, both encoders will be seeing the clock track and both DPLL&#39;s will be locked. During the final phase of the print only the second encoder will be seeing the clock track and only the second DPLL  443  will be locked. 
   During the initial phase the output from the first DPLL  440  must be used to generate the line sync signal  476 , but before the end of the middle phase the decoder must start using the output from the second DPLL  444  to generate the line sync signal  476 . Since it is not generally practical to space the encoders an integer number of clock periods apart, the output from the second DPLL  444  must be phase-aligned with the output of the first DPLL  443  before the transition occurs. 
   For the purposes of managing the transition, there are four clock tracking phases of interest. During the first phase, when only the first DPLL  443  is locked, the clock from the first DPLL  443  is selected via a multiplexer  462  and fed to the line sync generator  448 . During the second phase, which starts when the second DPLL  444  locks, the phase difference between the two DPLLs is computed  441  and latched into a phase difference register  445 . During the third phase, which starts a fixed time after the start of the second phase, the signal from the second DPLL  444 , is fed through a delay  447  set by the latched phase difference in the latch register  445 . During the fourth phase, which starts a fixed time after the start of the third phase, the delayed clock from the second DPLL  447  is selected via the multiplexer  462  and fed to the line sync generator  448 . 
     FIG. 64  shows the signals which control the clock tracking phases. The lock signals  449  and  451  are generated using lock detection circuits in the DPLL&#39;s  443  and  444 . Alternatively, PLL lock is assumed according to approximate knowledge of the position of the card relative to the two encoders  440  and  464 . The two phase control signals  453  and  455  are triggered by the lock signals  449  and  451  and controlled by timers. 
   Note that in practice, rather than explicitly delaying the second PLL&#39;s clock, the delayed clock can be generated directly by a digital oscillator which takes into account the phase difference. 
   Projecting the card  226  past the printhead  202  by momentum, permits a compact single drive shaft design. However, the deceleration of the card  226  once it disengages from the drive shaft  178  makes the generation of an accurate line sync signal  476  for the trailing edge much more difficult. If the compactness of the device is not overly critical, a second drive shaft after the printhead can keep the speed of the card constant until printing is complete. A drive system of this type is described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,167. In the interests of brevity, the disclosure of application Ser. No. 11/124,167 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Media Coding 
   The card  226  shown in  FIG. 54  has coded data in the form of the clock track  434 , the data track  436  and the Netpage tag pattern  438 . This coded data can serve a variety of functions and these are described below. However, the functions listed below are not exhaustive and the coded media (together with the appropriate mobile telecommunications device) can implement many other functions as well. Similarly, it is not necessary for all of these features to be incorporated into the coded data on the media. Any one or more can be combined to suit the application or applications for which a particular print medium and/or system is designed. 
   Side 
   The card can be coded to allow the printer to determine, prior to commencing printing, which side of the card is facing the printhead, i.e. the front or the back. This allows the printer to reject the card if it is inserted back-to-front, in case the card has been pre-printed with graphics on the back (e.g. advertising), or in case the front and the back have different surface treatments (e.g. to protect the graphics pre-printed on the back and/or to facilitate high-quality printing on the front). It also allows the printer to print side-dependent content (e.g. a photo on the front and corresponding photo details on the back). 
   Orientation 
   The card can be coded to allow the printer to determine, prior to commencing printing, the orientation of the card in relation to the printhead. This allows the printhead to print graphics rotated to match the rotation of pre-printed graphics on the back. It also allows the printer to reject the card if it is inserted with the incorrect orientation (with respect to pre-printed graphics on the back). Orientation can be determined by detecting an explicit orientation indicator, or by using the known orientation of information printed for another purpose, such as Netpage tags or even pre-printed user information or advertising. 
   Media Type/Size 
   The card can be coded to allow the printer to determine, prior to commencing printing, the type of the card. This allows the printer to prepare print data or select a print mode specific to the media type, for example, color conversion using a color profile specific to the media type, or droplet size modulation according to the expected absorbance of the card. The card can be coded to allow the printer to determine, prior to commencing printing, the longitudinal size of the card. This allows the printer to print graphics formatted for the size of the card, for example, a panoramic crop of a photo to match a panoramic card. 
   Prior Printing 
   The card can be coded to allow the printer to determine, prior to commencing printing, if the side of the card facing the printhead is pre-printed. The printer can then reject the card, prior to commencing printing, if it is inserted with the pre-printed side facing the printhead. This prevents over-printing. It also allows the printer to prepare, prior to commencing printing, content which fits into a known blank area on an otherwise pre-printed side (for example, photo details on the back of a photo, printed onto a card with pre-printed advertising on the back, but with a blank area for the photo details). 
   The card can be coded to allow the printer to detect, prior to commencing printing, whether the side facing the printhead has already been printed on demand (as opposed to pre-printed). This allows the printer to reject the card, prior to commencing printing, if the side facing the printhead has already been printed on demand, rather than overprinting the already-printed graphics. 
   The card can be coded to allow the printer to determine, ideally prior to commencing printing, if it is an authorised card. This allows the printer to reject, ideally prior to commencing printing, an un-authorised card, as the quality of the card will then be unknown, and the quality of the print cannot be guaranteed. 
   Position 
   The card can be coded to allow the printer to determine, prior to commencing printing, the absolute longitudinal position of the card in relation to the printhead. This allows the printer to print graphics in registration with the card. This can also be achieved by other means, such as by directly detecting the leading edge of the card. 
   The card can be coded to allow the printer to determine, prior to commencing printing, the absolute lateral position of the card in relation to the printhead. This allows the printer to print graphics in registration with the card. This can also be achieved by other means, such as by providing a snug paper path, and/or by detecting the side edge(s) of the card. 
   The card can be coded to allow the printer to track, during printing, the longitudinal position of the card in relation to the printhead, or the longitudinal speed of the card in relation to the printhead. This allows the printer to print graphics in registration with the card. This can also be achieved by other means, such as by coding and tracking a moving part in the transport mechanism. 
   The card can be coded to allow the printer to track, during printing, the lateral position of the card in relation to the printhead, or the lateral speed of the card in relation to the printhead. This allows the printer to print graphics in registration with the card. This can also be achieved by other means, such as by providing a snug paper path, and/or by detecting the side edge(s) of the card. 
   Invisibility 
   The coding can be disposed on or in the card so as to render it substantially invisible to an unaided human eye. This prevents the coding from detracting from printed graphics. 
   Fault Tolerance 
   The coding can be sufficiently fault-tolerant to allow the printer to acquire and decode the coding in the presence of an expected amount of surface contamination or damage. This prevents an expected amount of surface contamination or damage from causing the printer to reject the card or from causing the printer to produce a sub-standard print. 
   In light of the broad ranging functionality that a suitable M-Print printer with compatible cards can provide, several design alternatives for the printer, the cards and the coding are described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/125,167. In the interests of brevity, the disclosure of application Ser. No. 11/124,167 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Linear Encoding 
   Kip is the assignee&#39;s internal name for a template for a class of robust one-dimensional optical encoding schemes for storing small quantities of digital data on physical surfaces. It optionally incorporates error correction to cope with real-world surface degradation. 
   A particular encoding scheme is defined by specializing the Kip template described below. Parameters include the data capacity, the clocking scheme, the physical scale, and the level of redundancy. A Kip reader is typically also specialized for a particular encoding scheme. 
   A Kip encoding is designed to be read via a simple optical detector during transport of the encoded medium past the detector. The encoding therefore typically runs parallel to the transport direction of the medium. For example, a Kip encoding may be read from a print medium during printing. In the preferred embodiment, Kip encoded data is provided along at least one (and preferably two or more) of the longitudinal edges of the print media to be printed in a mobile device, as described above. In the preferred form, the Kip encoded data is printed in infrared ink, rendering it invisible or at least difficult to see with the unaided eye. 
   A Kip encoding is typically printed onto a surface, but may be disposed on or in a surface by other means. 
   Summary of Kip Parameters 
   The following tables summarize the parameters required to specialize Kip. The parameters should be understood in the context of the entire document. 
   The following table summarizes framing parameters: 
   
     
       
             
             
             
             
           
         
             
                 
                 
             
             
                 
               parameter 
               units 
               description 
             
             
                 
                 
             
           
           
             
                 
               L data   
               bits 
               Length of bitstream data. 
             
             
                 
                 
             
           
        
       
     
   
   The following table summarizes clocking parameters: 
   
     
       
             
             
             
           
         
             
                 
             
             
               parameter 
               units 
               description 
             
             
                 
             
           
           
             
               b clock   
               {0, 1} 
               Flag indicating whether the clock is implicit (0) or 
             
             
                 
                 
               explicit (1). 
             
             
               C clocksync   
               clock 
               Length of clock synchronization interval required 
             
             
                 
               periods 
               before data. 
             
             
                 
             
           
        
       
     
   
   The following table summarizes physical parameters: 
   
     
       
             
             
             
           
         
             
                 
             
             
               Parameter 
               Units 
               Description 
             
             
                 
             
           
           
             
               l clock   
               mm 
               Length of clock period. 
             
             
               l mark   
               mm 
               Length of mark. 
             
             
               l preamble   
               mm 
               Length of preamble. Equals or exceeds decoder&#39;s 
             
             
                 
                 
               uncertainty in longitudinal position of strip. 
             
             
               w mintrack   
               mm 
               Minimum width of track. 
             
             
               w misreg   
               mm 
               Maximum lateral misregistration of strip 
             
             
                 
                 
               with respect to reader. 
             
             
               α 
               radians 
               Maximum rotation of strip with respect to reader. 
             
             
                 
             
           
        
       
     
   
   The following table summarizes error correction parameters: 
                                   Parameter   Units   Description                   m   bits   Size of Reed-Solomon symbol.       k   symbols   Size of Reed-Solomon codeword data.       t   symbols   Error-correcting capacity of Reed-Solomon code.                    
Kip Encoding
 
   A Kip encoding encodes a single bitstream of data, and includes a number of discrete and independent layers, as illustrated in  FIG. 65 . The framing layer frames the bitstream to allow synchronization and simple error detection. The modulation and clocking layer encodes the bits of the frame along with clocking information to allow bit recovery. The physical layer represents the modulated and clocked frame using optically-readable marks. 
   An optional error correction layer encodes the bitstream to allow error correction. An application can choose to use the error correction layer or implement its own. 
   A Kip encoding is designed to allow serial decoding and hence has an implied time dimension. By convention in this document the time axis points to the right. However, a particular Kip encoding may be physically represented at any orientation that suits the application. 
   Framing 
   A Kip frame consists of a preamble, a pilot, the bitstream data itself, and a cyclic redundancy check (CRC) word, as illustrated in  FIG. 66 . 
   The preamble consists of a sequence of zeros of length L preamble . The preamble is long enough to allow the application to start the Kip decoder somewhere within the preamble, i.e. it is long enough for the application to know a priori the location of at least part of the preamble. The length of the preamble sequence in bits is therefore derived from an application-specific preamble length l preamble  (see EQ8). 
   The pilot consists of a unique pattern that allows the decoder to synchronize with the frame. The pilot pattern is designed to maximize its binary Hamming distance from arbitrary shifts of itself prefixed by preamble bits. This allows the decoder to utilize a maximum-likelihood decoder to recognize the pilot, even in the presence of bit errors. 
   The preamble and pilot together guarantee that any bit sequence the decoder detects before it detects the pilot is maximally separated from the pilot. 
   The pilot sequence is 1110 1011 01100010. Its length L pilot  is 16. Its minimum distance from preamble-prefixed shifts of itself is 9. It can therefore be recognized reliably in the presence of up to 4 bit errors. 
   The length L data  of the bitstream is known a priori by the application and is therefore a parameter. It is not encoded in the frame. The bitstream is encoded most-significant bit first, i.e. leftmost. 
   The CRC (cyclic redundancy code) is a CCITT CRC-16 (known to those skilled in the art, and so not described in detail here) calculated on the bitstream data, and allows the decoder to determine if the bitstream has been corrupted. 
   The length L CRC  of the CRC is 16. The CRC is calculated on the bitstream from left to right. The bitstream is padded with zero bits during calculation of the CRC to make its length an integer multiple of 8 bits. The padding is not encoded in the frame. 
   The length of a frame in bits is:
 
 L   frame   =L   preamble   +L   pilot   +L   data   +L   CRC   (EQ 1)
 
 L   frame   =L   preamble   +L   data +32  (EQ 2)
 
Modulation and Clocking
 
   The Kip encoding modulates the frame bit sequence to produce a sequence of abstract marks and spaces. These are realized physically by the physical layer. 
   The Kip encoding supports both explicit and implicit clocking. When the frame is explicitly clocked, the encoding includes a separate clock sequence encoded in parallel with the frame, as illustrated in  FIG. 67 . The bits of the frame are then encoded using a conventional non-return-to-zero (NRZ) encoding. A zero bit is represented by a space, and a one bit is represented by a mark. 
   The clock itself consists of a sequence of alternating marks and spaces. The center of a clock mark is aligned with the center of a bit in the frame. The frame encodes two bits per clock period, i.e. the bitrate of the frame is twice the rate of the clock. 
   The clock starts a number of clock periods C clocksync  before the start of the frame to allow the decoder to acquire clock synchronization before the start of the frame. The size of C clocksync  depends on the characteristics of the PLL used by the decoder, and is therefore a reader-specific parameter. 
   When the encoding is explicitly clocked, the corresponding decoder incorporates an additional optical sensor to sense the clock. 
   When the frame is implicitly clocked, the bits of the frame are encoded using a Manchester phase encoding. A zero bit is represented by space-mark transition, and a one bit is represented by mark-space transition, with both transitions defined left-to-right. The Manchester phase encoding allows the decoder to extract the clock signal from the modulated frame. 
   In this case the preamble is extended by C clocksync  bits to allow the decoder to acquire clock synchronization before searching for the pilot. 
   Assuming the same marking frequency, the bit density of the explicitly-clocked encoding is twice the bit density of the implicitly-clocked encoding. 
   The choice between explicit and implicit clocking depends on the application. Explicit clocking has the advantage that it provides greater longitudinal data density than implicit clocking. Implicit clocking has the advantage that it only requires a single optical sensor, while explicit clocking requires two optical sensors. 
   The parameter b clock  indicates whether the clock is implicit (b clock =0) or explicit (b clock =1). 
   The length, in clock periods, of the modulated and clocked Kip frame is:
 
 C   frame   =C   clocksync   +L   frame /(1+ b   clock )  (EQ 3)
 
Physical Representation
 
   The Kip encoding represents the modulated and clocked frame physically as a strip that has both a longitudinal extent (i.e. in the coding direction) and a lateral extent. 
   A Kip strip always contains a data track. It also contains a clock track if it is explicitly clocked rather than implicitly clocked. 
   The clock period l clock  within a Kip strip is nominally fixed, although a particular decoder will typically be able to cope with a certain amount of jitter and drift. Jitter and drift may also be introduced by the transport mechanism in a reader. The amount of jitter and drift supported by a decoder is decoder specific. 
   A suitable clock period depends on the characteristics of the medium and the marking mechanism, as well as on the characteristics of the reader. It is therefore an application-specific parameter. 
   Abstract marks and spaces have corresponding physical representations which give rise to distinct intensities when sampled by a matched optical sensor, allowing the decoder to distinguish marks and spaces. The spectral characteristics of the optical sensor, and hence the corresponding spectral characteristics of the physical marks and spaces, are application specific. 
   The transition time between a mark and a space is nominally zero, but is allowed to be up to 5% of the clock period. 
   An abstract mark is typically represented by a physical mark printed using an ink with particular absorption characteristics, such as an infrared-absorptive ink, and an abstract space is typically represented by the absence of such a physical mark, i.e. by the absorption characteristics of the substrate, such as broadband reflective (white) paper. However, Kip does not prescribe this. 
   The length l mark  of a mark and length l space  of a space are nominally the same. Suitable marks and spaces depend on the characteristics of the medium and the marking mechanism, as well as on the characteristics of the reader. Their lengths are therefore application-specific parameters. 
   The length of a mark and the length of a space may differ by up to a factor of ((2+(√{square root over (2)}−1))/(2−(√{square root over (2)}−1))) to accommodate printing of marks at up to half the maximum dot resolution of a particular printer, as illustrated in  FIG. 69 . The factor may vary between unity and the limit according to vertical position, as illustrated in the figure. 
   The sum of the length of a mark and the length of a space equals the clock period:
 
 l   clock   =l   mark   +l   space   (EQ 4)
 
   The overall length of the strip is:
 
 l   strip   =l   clock   ×C   frame   (EQ 5)
 
   The minimum width w mintrack  of a data track (or clock track) within a strip depends on the reader. It is therefore an application-specific parameter. 
   The required width w track  of a data track (or clock track) within a strip is determined by the maximum allowable lateral misregistration w misreg  and maximum allowable rotation α of the strip with respect to the transport path past the corresponding optical sensor:
 
 w   track   =w   mintrack   +w   misreg   +l   strip  tan α  (EQ 6)
 
   The maximum lateral misregistration and rotation depend on the characteristics of the medium and the marking mechanism, as well as on the characteristics of the reader. They are therefore application-specific parameters. 
   The width of a strip is:
 
 w   strip =(1+ b   clock )× w   track   (EQ 7)
 
   The length of the preamble sequence in bits is derived from a parameter which specifies the length of the preamble: 
                   L   preamble     =       ⌈       I   preamble       I   clock       ⌉     ×     (     1   +     b   clock       )               (     EQ   ⁢           ⁢   8     )               
Error Correction
 
   The Kip encoding optionally includes error correcting coding (ECC) information to allow the decoder to correct bitstream data corrupted by surface damage or dirt. Reed-Solomon redundancy data is appended to the frame to produce an extended frame, as illustrated in  FIG. 70 . 
   A Kip Reed-Solomon code is characterized by its symbol size m (in bits), data size k (in symbols), and error-correcting capacity t (in symbols), as described below. A Reed-Solomon code is chosen according to the size L data  of the bitstream data and the expected bit error rate. The parameters of the code are therefore application-specific. 
   Redundancy data is calculated on the concatenation of the bitstream data and the CRC. This allows the CRC to be corrected as well. 
   The bitstream data and the CRC are padded with zero bits during calculation of the redundancy data to make their length an integer multiple of the symbol size m. The padding is not encoded in the extended frame. 
   A decoder verifies the CRC before performing Reed-Solomon error correction. If the CRC is valid, then error correction may potentially be skipped. If the CRC is invalid, then the decoder performs error correction. It then verifies the CRC again to check that error correction succeeded. 
   The length of a Reed-Solomon codeword in bits is:
 
 L   codeword =(2 t+k )× m   (EQ 9)
 
   The number of Reed-Solomon codewords is: 
   
     
       
         
           
             
               
                 s 
                 = 
                 
                   
                     
                       
                         ( 
                         
                           
                             L 
                             data 
                           
                           + 
                           
                             L 
                             CRC 
                           
                         
                         ) 
                       
                       - 
                       1 
                     
                     
                       L 
                       codeword 
                     
                   
                   + 
                   1 
                 
               
             
             
               
                 ( 
                 
                   EQ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   10 
                 
                 ) 
               
             
           
         
       
     
   
   The length of the redundancy data is:
 
 L   ECC   =s×( 2 t×m )  (EQ 11)
 
   The length of an extended frame in bits is:
 
 L   extendedframe   =L   frame   +L   ECC   (EQ 12)
 
Reed-Solomon Coding
 
   A  2   m -ary Reed-Solomon code (n, k) is characterized by its symbol size m (in bits), codeword size n (in symbols), and data size k (in symbols), where:
 
 n= 2 m −1  (EQ 13)
 
   The error-correcting capacity of the code is t symbols, where: 
   
     
       
         
           
             
               
                 t 
                 = 
                 
                   ⌊ 
                   
                     
                       n 
                       - 
                       k 
                     
                     2 
                   
                   ⌋ 
                 
               
             
             
               
                 ( 
                 
                   EQ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   14 
                 
                 ) 
               
             
           
         
       
     
   
   To minimize the redundancy overhead of a given error-correcting capacity, the number of redundancy symbols n−k is chosen to be even, i.e. so that:
 
2 t=n−k   (EQ 15)
 
   Reed-Solomon codes are well known and understood in the art of data storage, and so are not described in great detail here. 
   Data symbols d i  and redundancy symbols r j  of the code are indexed from left to right according to the power of their corresponding polynomial terms, as illustrated in  FIG. 71 . Note that data bits are indexed in the opposite direction, i.e. from right to left. 
   The data capacity of a given code may be reduced by puncturing the code, i.e. by systematically removing a subset of data symbols. Missing symbols can then be treated as erasures during decoding. In this case:
 
 n=k+ 2 t&lt; 2 m −1  (EQ 16)
 
   Longer codes and codes with greater error-correcting capacities are computationally more expensive to decode than shorter codes or codes with smaller error-correcting capacities. Where application constraints limit the complexity of the code and the required data capacity exceeds the capacity of the chosen code, multiple codewords can be used to encode the data. To maximize the codewords&#39; resilience to burst errors, the codewords are interleaved. 
   To maximize the utility of the Kip encoding, the bitstream is encoded contiguously and in order within the frame. To reconcile the requirement for interleaving and the requirement for contiguity and order, the bitstream is de-interleaved for the purpose of computing the Reed-Solomon redundancy data, and is then re-interleaved before being encoded in the frame. This maintains the order and contiguity of the bitstream, and produces a separate contiguous block of interleaved redundancy data which is placed at the end of the extended frame. The Kip interleaving scheme is defined in detail below. 
   Kip Reed-Solomon codes have the primitive polynomials given in the following table: 
   
     
       
             
             
           
             
             
           
         
             
                 
             
             
               Symbol size 
                 
             
             
               (m) 
               Primitive polynomial 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               3 
               1011 
             
             
               4 
               10011 
             
             
               5 
               100101 
             
             
               6 
               1000011 
             
             
               7 
               10000011 
             
             
               8 
               101110001 
             
             
               9 
               1000010001 
             
             
               10 
               10000001001 
             
             
               11 
               100000000101 
             
             
               12 
               1000001010011 
             
             
               13 
               10000000011011 
             
             
               14 
               100000001010011 
             
             
                 
             
           
        
       
     
   
   The entries in the table indicate the coefficients of the primitive polynomial with the highest-order coefficient on the left. Thus the primitive polynomial for m=4 is:
 
p( x )= x   4   +x+ 1  (EQ 17)
 
   Kip Reed-Solomon codes have the following generator polynomials: 
   
     
       
         
           
             
               
                 
                   g 
                   ⁡ 
                   
                     ( 
                     x 
                     ) 
                   
                 
                 = 
                 
                   
                     
                       ( 
                       
                         x 
                         + 
                         α 
                       
                       ) 
                     
                     ⁢ 
                     
                       ( 
                       
                         x 
                         + 
                         
                           α 
                           2 
                         
                       
                       ) 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     … 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ( 
                       
                         x 
                         + 
                         
                           α 
                           
                             2 
                             ⁢ 
                             t 
                           
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       ∏ 
                       
                         i 
                         = 
                         1 
                       
                       
                         2 
                         ⁢ 
                         t 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         x 
                         + 
                         
                           α 
                           i 
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 ( 
                 
                   EQ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   18 
                 
                 ) 
               
             
           
         
       
     
   
   For the purposes of interleaving, the source data D is partitioned into a sequence of m-bit symbols and padded on the right with zero bits to yield a sequence of u symbols, consisting of an integer multiple s of k symbols, where s is the number of codewords:
 
 u=s×k   (EQ 19)
 
D={D 0 , . . . , D u−1 }  (EQ 20)
 
   Each symbol in this sequence is then mapped to a corresponding (i th ) symbol d w, i  of an interleaved codeword w:
 
 d   w, i   =D   (i×s)+w   (EQ 21)
 
   The resultant interleaved data symbols are illustrated in  FIG. 72 . Note that this is an in situ mapping of the source data to codewords, not a re-arrangement of the source data. 
   The symbols of each codeword are de-interleaved prior to encoding the codeword, and the resultant redundancy symbols are re-interleaved to form the redundancy block. The resultant interleaved redundancy symbols are illustrated in  FIG. 73 . 
   General Netpage Description 
   Netpage interactivity can be used to provide printed user interfaces to various phone functions and applications, such as enabling particular operational modes of the mobile telecommunications device or interacting with a calculator application, as well as providing general “keypad”, “keyboard” and “tablet” input to the mobile telecommunications device. Such interfaces can be pre-printed and bundled with a phone, purchased separately (as a way of customizing phone operation, similar to ringtones and themes) or printed on demand where the phone incorporates a printer. 
   A printed Netpage business card provides a good example of how a variety of functions can be usefully combined in a single interface, including:
         loading contact details into an address book   displaying a Web page   displaying an image   dialing a contact number   bringing up an e-mail, SMS or MMS form   loading location info into a navigation system   activating a promotion or special offer       

   Any of these functions can be made single-use only. 
   A business card may be printed by the mobile telecommunications device user for presentation to someone else, or may be printed from a Web page relating to a business for the mobile telecommunications device user&#39;s own use. It may also be pre-printed. 
   As described below, the primary benefit of incorporating a Netpage pointer or pen in another device is synergy. A Netpage pointer or pen incorporated in a mobile phone, smartphone or telecommunications-enabled PDA, for example, allows the device to act as both a Netpage pointer and as a relay between the pointer and the mobile phone network and hence a Netpage server. When the pointer is used to interact with a page, the target application of the interaction can display information on the phone display and initiate further interaction with the user via the phone touchscreen. The pointer is most usefully configured so that its “nib” is in a corner of the phone body, allowing the user to easily manipulate the phone to designate a tagged surface. 
   The phone can incorporate a marking nib and optionally a continuous force sensor to provide full Netpage pen functionality. 
   An exemplary Netpage interaction will now be described to show how a sensing device in the form of a Netpage enabled mobile device interacts with the coded data on a print medium in the form of a card. Whilst in the preferred form the print medium is a card generated by the mobile device or another mobile device, it can also be a commercially pre-printed card that is purchased or otherwise provided as part of a commercial transaction. The print medium can also be a page of a book, magazine, newspaper or brochure, for example. 
   The mobile device senses a tag using an area image sensor and detects tag data. The mobile device uses the sensed data tag to generate interaction data, which is sent via a mobile telecommunications network to a document server. The document server uses the ID to access the document description, and interpret the interaction. In appropriate circumstances, the document server sends a corresponding message to an application server, which can then perform a corresponding action. 
   Typically Netpage pen and Netpage-enabled mobile device users register with a registration server, which associates the user with an identifier stored in the respective Netpage pen or Netpage enabled mobile device. By providing the sensing device identifier as part of the interaction data, this allows users to be identified, allowing transactions or the like to be performed. 
   Netpage documents are generated by having an ID server generate an ID which is transferred to the document server. The document server determines a document description and then records an association between the document description and the ID, to allow subsequent retrieval of the document description using the ID. 
   The ID is then used to generate the tag data, as will be described in more detail below, before the document is printed by a suitable printer, using the page description and the tag map. 
   Each tag is represented by a pattern which contains two kinds of elements. The first kind of element is a target. 
   Targets allow a tag to be located in an image of a coded surface, and allow the perspective distortion of the tag to be inferred. The second kind of element is a macrodot. Each macrodot encodes the value of a bit by its presence or absence. 
   The pattern is represented on the coded surface in such a way as to allow it to be acquired by an optical imaging system, and in particular by an optical system with a narrowband response in the near-infrared. The pattern is typically printed onto the surface using a narrowband near-infrared ink. 
   In the preferred embodiment, the region typically corresponds to the entire surface of an M-Print card, and the region ID corresponds to the unique M-Print card ID. For clarity in the following discussion we refer to items and IDs, with the understanding that the ID corresponds to the region ID. 
   The surface coding is designed so that an acquisition field of view large enough to guarantee acquisition of an entire tag is large enough to guarantee acquisition of the ID of the region containing the tag. Acquisition of the tag itself guarantees acquisition of the tag&#39;s two-dimensional position within the region, as well as other tag-specific data. The surface coding therefore allows a sensing device to acquire a region ID and a tag position during a purely local interaction with a coded surface, e.g. during a “click” or tap on a coded surface with a pen. 
   Example Tag Structure 
   A wide range of different tag structures (as described in the assignee&#39;s various cross-referenced Netpage applications) can be used. The preferred tag will now be described in detail. 
     FIG. 74  shows the structure of a complete tag  1400 . Each of the four black circles  1402  is a target. The tag  1400 , and the overall pattern, has four-fold rotational symmetry at the physical level. Each square region  1404  represents a symbol, and each symbol represents four bits of information. 
     FIG. 75  shows the structure of a symbol. It contains four macrodots  1406 , each of which represents the value of one bit by its presence (one) or absence (zero). The macrodot spacing is specified by the parameter s throughout this document. It has a nominal value of 143 μm, based on 9 dots printed at a pitch of 1600 dots per inch. However, it is allowed to vary by ±10% according to the capabilities of the device used to produce the pattern. 
     FIG. 76  shows an array of nine adjacent symbols. The macrodot spacing is uniform both within and between symbols. 
     FIG. 77  shows the ordering of the bits within a symbol. Bit zero (b 0 ) is the least significant within a symbol; bit three (b 3 ) is the most significant. Note that this ordering is relative to the orientation of the symbol. The orientation of a particular symbol within the tag  1400  is indicated by the orientation of the label of the symbol in the tag diagrams. In general, the orientation of all symbols within a particular segment of the tag have the same orientation, consistent with the bottom of the symbol being closest to the centre of the tag. 
   Only the macrodots  1406  are part of the representation of a symbol in the pattern. The square outline  1404  of a symbol is used in this document to more clearly elucidate the structure of a tag  1400 .  FIG. 78 , by way of illustration, shows the actual pattern of a tag  1400  with every bit set. Note that, in practice, every bit of a tag  1400  can never be set. 
   A macrodot  1406  is nominally circular with a nominal diameter of ( 5/9)s. However, it is allowed to vary in size by ±10% according to the capabilities of the device used to produce the pattern. 
   A target  1402  is nominally circular with a nominal diameter of ( 17/9)s. However, it is allowed to vary in size by ±10% according to the capabilities of the device used to produce the pattern. 
   The tag pattern is allowed to vary in scale by up to ±10% according to the capabilities of the device used to produce the pattern. Any deviation from the nominal scale is recorded in the tag data to allow accurate generation of position samples. 
   Each symbol shown in the tag structure in  FIG. 74  has a unique label. Each label consists an alphabetic prefix and a numeric suffix. 
   Tag Group 
   Tags are arranged into tag groups. Each tag group contains four tags arranged in a square. Each tag therefore has one of four possible tag types according to its location within the tag group square. The tag types are labelled  00 ,  10 ,  01  and  11 , as shown in  FIG. 79 . 
     FIG. 80  shows how tag groups are repeated in a continuous tiling of tags. The tiling guarantees the any set of four adjacent tags contains one tag of each type. 
   Codewords 
   The tag contains four complete codewords. Each codeword is of a punctured 24-ary (8,5) Reed-Solomon code. Two of the codewords are unique to the tag. These are referred to as local and are labelled A and B. The tag therefore encodes up to 40 bits of information unique to the tag. 
   The remaining two codewords are unique to a tag type, but common to all tags of the same type within a contiguous tiling of tags. These are referred to as global and are labelled C and D, subscripted by tag type. A tag group therefore encodes up to 160 bits of information common to all tag groups within a contiguous tiling of tags. The layout of the four codewords is shown in  FIG. 81 . 
   Reed-Solomon Encoding 
   Codewords are encoded using a punctured 24-ary (8,5) Reed-Solomon code. A 24-ary (8,5) Reed-Solomon code encodes 20 data bits (i.e. five 4-bit symbols) and 12 redundancy bits (i.e. three 4-bit symbols) in each codeword. Its error-detecting capacity is three symbols. Its error-correcting capacity is one symbol. More information about Reed-Solomon encoding in the Netpage context is provide in U.S. Ser. No. 10/815,647, filed on Apr. 2, 2004, the contents of which are herein incorporated by cross-reference. 
   Netpage in a Mobile Environment 
     FIG. 82  provides an overview of the architecture of the Netpage system, incorporating local and remote applications and local and remote Netpage servers. The generic Netpage system is described extensively in many of the assignee&#39;s patents and co-pending applications, (such as U.S. Ser. No. 09/722,174, filed on Nov. 25, 2000), and so is not described in detail here. However, a number of extensions and alterations to the generic Netpage system are used as part of implementing various Netpage-based functions into a mobile device. This applies both to Netpage-related sensing of coded data on a print medium being printed (or about to be printed) and to a Netpage-enabled mobile device with or without a printer. 
   Referring to  FIG. 82 , a Netpage microserver  790  running on the mobile phone  1  provides a constrained set of Netpage functions oriented towards interpreting clicks rather than interpreting general digital ink. When the microserver  790  accepts a click event from the pointer driver  718  it interprets it in the usual Netpage way. This includes retrieving the page description associated with the click impression ID, and hit testing the click location against interactive elements in a page description. This may result in the microserver identifying a command element and sending the command to the application specified by the command element. This functionality is described in many of the earlier Netpage applications cross-referenced above. 
   The target application may be a local application  792  or a remote application  700  accessible via the network  788 . The microserver  790  may deliver a command to a running application or may cause the application to be launched if not already running. 
   If the microserver  790  receives a click for an unknown impression ID, then it uses the impression ID to identify a network-based Netpage server  798  capable of handling the click, and forwards the click to that server for interpretation. The Netpage server  798  may be on a private intranet accessible to the mobile telecommunications device, or may be on the public Internet. 
   For a known impression ID the microserver  790  may interact directly with a remote application  700  rather than via the Netpage server  798 . 
   In the event that the mobile device includes a printer  4 , an optional printing server  796  is provided. The printing server  796  runs on the mobile phone  1  and accepts printing requests from remote applications and Netpage servers. When the printing server accepts a printing request from an untrusted application, it may require the application to present a single-use printing token previously issued by the mobile telecommunications device. 
   A display server  704  running on the mobile telecommunications device accepts display requests from remote applications and Netpage servers. When the display server  704  accepts a display request from an untrusted application, it may require the application to present a single-use display token previously issued by the mobile telecommunications device. The display server  704  controls the mobile telecommunications device display  750 . 
   As illustrated in  FIG. 83 , the mobile telecommunications device may act as a relay for a Netpage stylus, pen, or other Netpage input device  708 . If the microserver  790  receives digital ink for an unknown impression ID, then it uses the impression ID to identify a network-based Netpage server  798  capable of handling the digital ink, and forwards the digital ink to that server for interpretation. 
   Although not required to, the microserver  790  can be configured to have some capability for interpreting digital ink. For example, it may be capable of interpreting digital ink associated with checkboxes and drawings fields only, or it may be capable of performing rudimentary character recognition, or it may be capable of performing character recognition with the help of a remote server. 
   The microserver can also be configured to enable routing of digital ink captured via a Netpage “tablet” to the mobile telecommunications device operating system. A Netpage tablet may be a separate surface, pre-printed or printed on demand, or it may be an overlay or underlay on the mobile telecommunications device display. 
   The Netpage pointer incorporates the same image sensor and image processing ASIC (referred to as “Jupiter”, and described in detail below) developed for and used by the Netpage pen. Jupiter responds to a contact switch by activating an illumination LED and capturing an image of a tagged surface. It then notifies the mobile telecommunications device processor of the “click”. The Netpage pointer incorporates a similar optical design to the Netpage pen, but ideally with a smaller form factor. The smaller form factor is achieved with a more sophisticated multi-lens design, as described below. 
   Obtaining Media Information Directly from Netpage Tags 
   Media information can be obtained directly from the Netpage tags. It has the advantage that no data track is required, or only a minimal data track is required, since the Netpage identifier and digital signatures in particular can be obtained from the Netpage tag pattern. 
   The Netpage tag sensor is capable of reading a tag pattern from a snapshot image. This has the advantage that the image can be captured as the card enters the paper path, before it engages the transport mechanism, and even before the printer controller is activated, if necessary. 
   A Netpage tag sensor capable of reading tags as the media enters or passes through the media feed path is described in detail in the Netpage Clicker sub-section below (see  FIGS. 84 and 85 ). 
   Conversely, the advantage of reading the tag pattern during transport (either during a reading phase or during the printing phase), is that the printer can obtain exact information about the lateral and longitudinal registration between the Netpage tag pattern and the visual content printed by the printer. Whilst a single captured image of a tag can be used to determine registration in either or both directions, it is preferred to determine the registration based on at least two captured images. The images can be captured sequentially by a single sensor, or two sensors can capture them simultaneously or sequentially. Various averaging approaches can be taken to determine a more accurate position in either or both direction from two or more captured images than would be available by replying on a single image. 
   If the tag pattern can be rotated with respect to the printhead, either due to the manufacturing tolerances of the card itself or tolerances in the paper path, it is advantageous to read the tag pattern to determine the rotation. The printer can then report the rotation to the Netpage server, which can record it and use it when it eventually interprets digital ink captured via the card. Whilst a single captured image of a tag can be used to determine the rotation, it is preferred to determine the rotation based on at least two captured images. The images can be captured sequentially by a single sensor, or two sensors can capture them simultaneously or sequentially. Various averaging approaches can be taken to determine a more accurate rotation from two or more captured images than would be available by replying on a single image. 
   Netpage Options 
   The following media coding options relate to the Netpage tags. Netpage is described in more detail in a later section. 
   Netpage Tag Orientation 
   The card can be coded to allow the printer to determine, possibly prior to commencing printing, the orientation of Netpage tags on the card in relation to the printhead. This allows the printer to rotate page graphics to match the orientation of the Netpage tags on the card, prior to commencing printing. It also allows the printer to report the orientation of the Netpage tags on the card for recording by a Netpage server. 
   Netpage Tag Position 
   If lateral and longitudinal registration and motion tracking, as discussed above, is achieved by means other than via the media coding, then any misregistration between the media coding itself and the printed content, either due to manufacturing tolerances in the card itself or due to paper path tolerances in the printer, can manifest themselves as a lateral and/or longitudinal registration error between the Netpage tags and the printed content. This in turn can lead to a degraded user experience. For example, if the zone of a hyperlink may fail to register accurately with the visual representation of the hyperlink. 
   As discussed above in relation to card position, the media coding can provide the basis for accurate lateral and longitudinal registration and motion tracking of the media coding itself, and the printer can report this registration to the Netpage server alongside the Netpage identifier. The Netpage server can record this registration information as a two-dimensional offset which corrects for any deviation between the nominal and actual registration, and correct any digital ink captured via the card accordingly, before interpretation. 
   Netpage Identity 
   The card can be coded to allow the printer to determine the unique 96-bit Netpage identifier of the card. This allows the printer to report the Netpage identifier of the card for recording by a Netpage server (which associates the printed graphics and input description with the identity). 
   The card can be coded to allow the printer to determine the unique Netpage identifier of the card from either side of the card. This allows printer designers the flexibility of reading the Netpage identifier from the most convenient side of the card. 
   The card can be coded to allow the printer to determine if it is an authorised Netpage card. This allows the printer to not perform the Netpage association step for an un-authorised card, effectively disabling its Netpage interactivity. This prevents a forged card from preventing the use of a valid card with the same Netpage identifier. 
   The card can be coded to allow the printer to determine both the Netpage identifier and a unique digital signature associated with the Netpage identifier. This allows the printer to prevent forgery using a digital signature verification mechanism already in place for the purpose of controlling interactions with Netpage media. 
   Netpage Interactivity 
   Substantially all the front side of the card can be coded with Netpage tags to allow a Netpage sensing device to interact with the card subsequent to printing. This allows the printer to print interactive Netpage content without having to include a tag printing capability. If the back side of the card is blank and printable, then substantially the entire back side of the card can be coded with Netpage tags to allow a Netpage sensing device to interact with the card subsequent to printing. This allows the printer to print interactive Netpage content without having to include a tag printing capability. 
   The back side of the card can be coded with Netpage tags to allow a Netpage sensing device to interact with the card. This allows interactive Netpage content to be pre-printed on the back of the card. 
   Cryptography 
   Blank media designed for use with the preferred embodiment are pre-coded to satisfy a number of requirements, supporting motion sensing and Netpage interactivity, and protecting against forgery. 
   The Applicant&#39;s co-pending application Ser. No. 11/124,167 describes authentication mechanisms that can be used to detect and reject forged or un-coded blank media. The co-pending application is one of the above listed cross referenced documents whose disclosures are incorporated herein. 
   Netpage Clicker 
   An alternative embodiment of the invention is shown in  FIGS. 84 and 85 , in which the mobile device includes a Netpage clicker module  362 . This embodiment includes a printer and uses a dual optical pathway arrangement to sense coded data from media outside the mobile device as well as coded data pre-printed on media as it passes through the device for printing. 
   The Netpage clicker in the preferred embodiment forms part of a dual optical path Netpage sensing device. The first path is used in the Netpage clicker, and the second operates to read coded data from the card as it enters the mobile telecommunications device for printing. As described below, the coded data on the card is read to ensure that the card is of the correct type and quality to enable printing. 
   The Netpage clicker includes a non-marking nib  340  that exits the top of the mobile telecommunications device. The nib  340  is slidably mounted to be selectively moveable between a retracted position, and an extended position by manual operation of a slider  342 . The slider  342  is biased outwardly from the mobile telecommunications device, and includes a ratchet mechanism (not shown) for retaining the nib  340  in the extended position. To retract the nib  340 , the user depresses the slider  342 , which disengages the ratchet mechanism and enables the nib  340  to return to the retracted position. One end of the nib abuts a switch (not shown), which is operatively connected to circuitry on the PCB. 
   Working from one end of the first optical path to the other, a first infrared LED  344  is mounted to direct infrared light out of the mobile device via an aperture to illuminate an adjacent surface (not shown). Light reflected from the surface passes through an infrared filter  348 , which improves the signal to noise ratio of the reflected light by removing most non-infrared ambient light. The reflected light is focused via a pair of lenses  350  and then strikes a plate beam splitter  352 . It will be appreciated that the beam splitter  352  can include one or more thin-film optical coatings to improve its performance. 
   A substantial portion of the light is deflected downwardly by the plate splitter and lands on an image sensor  346  that is mounted on the PCB. The image sensor  346  in the preferred embodiment takes the form of the Jupiter image sensor and processor described in detail below. It will be appreciated that a variety of commercially available CCD and CMOS image sensors would also be suitable. 
   The particular position of the nib, and orientation and position of the first optical path within the casing enables a user to interact with Netpage interactive documents as described elsewhere in the detailed description. These Netpage documents can include media printed by the mobile device itself, as well as other media such as preprinted pages in books, magazines, newspapers and the like. 
   The second optical path starts with a second infrared LED  354 , which is mounted to shine light onto a surface of a card  226  when it is inserted in the mobile telecommunications device for printing. The light is reflected from the card  226 , and is turned along the optical path by a first turning mirror  356  and a second turning mirror  358 . The light then passes through an aperture  359  a lens  360  and the beam splitter  352  and lands on the image sensor  346 . 
   The mobile device is configured such that both LEDs  344  and  354  turned off when a card is not being printed and the nib is not being used to sense coded data on an external surface. However, once the nib is extended and pressed onto a surface with sufficient force to close the switch, the LED  344  is illuminated and the image sensor  346  commences capturing images. 
   Although a non-marking nib has been described, a marking nib, such as a ballpoint or felt-tip pen, can also be used. Where a marking nib is used, it is particularly preferable to provide the retraction mechanism to allow the nib to selectively be withdrawn into the casing. Alternatively, the nib can be fixed (ie, no retraction mechanism is provided). 
   In other embodiments, the switch is simply omitted (and the device operates continuously, preferably only when placed into a capture mode) or replaced with some other form of pressure sensor, such as a piezo-electric or semiconductor-based transducer. In one form, a multi-level or continuous pressure sensor is utilized, which enables capture of the actual force of the nib against the writing surface during writing. This information can be included with the position information that comprises the digital ink generated by the device, which can be used in a manner described in detail in many of the assignee&#39;s cross-referenced Netpage-related applications. However, this is an optional capability. 
   It will be appreciated that in other embodiments a simple Netpage sensing device can also be included in a mobile device that does not incorporate a printer. 
   In other embodiments, one or more of the turning mirrors can be replaced with one or more prisms that rely on boundary reflection or silvered (or half silvered) surfaces to change the course of light through the first or second optical paths. It is also possible to omit either of the first or second optical paths, with corresponding removal of the capabilities offered by those paths. 
   Image Sensor and Associated Processing Circuitry 
   In the preferred embodiment, the Netpage sensor is a monolithic integrated circuit that includes an image sensor, analog to digital converter (ADC), image processor and interface, which are configured to operate within a system including a host processor. The applicants have codenamed the monolithic integrated circuit “Jupiter”. The image sensor and ADC are codenamed “Ganymede” and the image processor and interface are codenamed “Callisto”. 
   In a preferred embodiment of the invention, the image sensor is incorporated in a Jupiter image sensor as described in co-pending application U.S. Ser. No. 10/778,056, filed on Feb. 17, 2004, the contents of which are incorporated herein by cross-reference. 
   Various alternative pixel designs suitable for incorporation in the Jupiter image sensor are described in PCT application PCT/AU/02/01573 entitled “Active Pixel Sensor”, filed 22 Nov. 2002; and PCT application PCT/AU02/01572 entitled “Sensing Device with Ambient Light Minimisation”, filed 22 Nov. 2002; the contents of which are incorporated herein by cross reference. 
   It should appreciated that the aggregation of particular components into functional or codenamed blocks is not necessarily an indication that such physical or even logical aggregation in hardware is necessary for the functioning of the present invention. Rather, the grouping of particular units into functional blocks is a matter of design convenience in the particular preferred embodiment that is described. The intended scope of the present invention embodied in the detailed description should be read as broadly as a reasonable interpretation of the appended claims allows. 
   Image Sensor 
   Jupiter comprises an image sensor array, ADC (Analog to Digital Conversion) function, timing and control logic, digital interface to an external microcontroller, and implementation of some of the computational steps of machine vision algorithms. 
     FIG. 86  shows a system-level diagram of the Jupiter monolithic integrated circuit  1601  and its relationship with a host processor  1602 . Jupiter  1601  has two main functional blocks: Ganymede  1604  and Callisto  1606 . As described below, Ganymede comprises a sensor array  1612 , ADC  1614 , timing and control logic  1616 , clock multiplier PLL  1618 , and bias control  1619 . Callisto comprises the image processing, image buffer memory, and serial interface to a host processor. A parallel interface  1608  links Ganymede  4  with Callisto  6 , and a serial interface  1610  links Callisto  1606  with the host processor  2 . 
   The internal interfaces in Jupiter are used for communication among the different internal modules. 
   Ganymede Image Sensor 
   Features 
   
       
       Sensor array 
       8-bit digitisation of the sensor array output 
       Ddigital image output to Callisto 
       Clock multiplying PLL 
     
  
   As shown in  FIG. 87 , Ganymede  1604  comprises a sensor array  1612 , an ADC block  1614 , a control and timing block  1616  and a clock-multiplying phase lock loop (PLL)  1618  for providing an internal clock signal. The sensor array  1612  comprises pixels  1620 , a row decoder  1622 , and a column decoder/MUX  1624 . The ADC block  1614  includes an 8-bit ADC  26  and a programmable gain amplifier (PGA)  1628 . The control and timing block  1616  controls the sensor array  1612 , the ADC  1614 , and the PLL  1618 , and provides an interface to Callisto  1606 . 
   Callisto 
   Callisto is an image processor  1625  designed to interface directly to a monochrome image sensor via a parallel data interface, optionally perform some image processing and pass captured images to an external device via a serial data interface. 
   Features 
   
       
       Parallel interface to image sensor 
       Frame store buffer to decouple parallel image sensor interface and external serial interface 
       Double buffering of frame store data to eliminate buffer loading overhead 
       Low pass filtering and sub-sampling of captured image 
       Local dynamic range expansion of sub-sampled image 
       Thresholding of the sub-sampled, range-expanded image 
       Read-out of pixels within a defined region of the captured image, for both processed and unprocessed images 
       Calculation of sub-pixel values 
       Configurable image sensor timing interface 
       Configurable image sensor size 
       Configurable image sensor window 
       Power management: auto sleep and wakeup modes 
       External serial interface for image output and device management 
       External register interface for register management on external devices
 
Environment
 
     
  
   Callisto interfaces to both an image sensor, via a parallel interface, and to an external device, such as a microprocessor, via a serial data interface. Captured image data is passed to Callisto across the parallel data interface from the image sensor. Processed image data is passed to the external device via the serial interface. Callisto&#39;s registers are also set via the external serial interface. 
   Function 
   The Callisto image processing core accepts image data from an image sensor and passes that data, either processed or unprocessed, to an external device using a serial data interface. The rate at which data is passed to that external device is decoupled from whatever data read-out rates are imposed by the image sensor. 
   The image sensor data rate and the image data rate over the serial interface are decoupled by using an internal RAM-based frame store. Image data from the sensor is written into the frame store at a rate to satisfy image sensor read-out requirements. Once in the frame store, data can be read out and transmitted over the serial interface at whatever rate is required by the device at the other end of that interface. 
   Callisto can optionally perform some image processing on the image stored in its frame store, as dictated by user configuration. The user may choose to bypass image processing and obtain access to the unprocessed image. Sub-sampled images are stored in a buffer but fully processed images are not persistently stored in Callisto; fully processed images are immediately transmitted across the serial interface. Callisto provides several image process related functions:
     Sub-sampling   Local dynamic range expansion   Thresholding   Calculation of sub-pixel values   Read-out of a defined rectangle from the processed and unprocessed image   

   Sub-sampling, local dynamic range expansion and thresholding are typically used in conjunction with dynamic range expansion performed on sub-sampled images, and thresholding performed on sub-sampled, range-expanded images. Dynamic range expansion and thresholding are performed together, as a single operation, and can only be performed on sub-sampled images. Sub-sampling, however, may be performed without dynamic range expansion and thresholding. Retrieval of sub-pixel values and image region read-out are standalone functions. 
   A number of specific alternative optics systems for sensing Netpage tags using the mobile device are described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,167. In the interests of brevity, the disclosure of application Ser. No. 11/124,167 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   The invention can also be embodied in a number of other form factors, one of which is a PDA. This embodiment is described in detail in the Applicant&#39;s co-pending application identified by application Ser. No. 11/124,167. In the interests of brevity, the disclosure of application Ser. No. 11/124,167 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   Another embodiment is the Netpage camera phone. Printing a photo as a Netpage and a camera incorporating a Netpage printer are both claimed in WO 00/71353 (NPA035), Method and System for Printing a Photograph and WO 01/02905 (NPP019), Digital Camera with Interactive Printer, the contents of which are incorporated herein by way of cross-reference. When a photo is captured and printed using a Netpage digital camera, the camera also stores the photo image persistently on a network server. The printed photo, which is Netpage tagged, can then be used as a token to retrieve the photo image. 
   A camera-enabled smartphone can be viewed as a camera with an in-built wireless network connection. When the camera-enabled smartphone incorporates a Netpage printer, as described above, it becomes a Netpage camera. 
   When the camera-enabled smartphone also incorporates a Netpage pointer or pen, as described above, the pointer or pen can be used to designate a printed Netpage photo to request a printed copy of the photo. The phone retrieves the original photo image from the network and prints a copy of it using its in-built Netpage printer. This is done by sending at least the identity of the printed document to a Netpage server. This information alone may be enough to allow the photo to be retrieved for display or printing. However, in the preferred embodiment, the identity is sent along with at least a position of the pen/clicker as determined 
   A mobile phone or smartphone Netpage camera can take the form of any of the embodiments described above that incorporate a printer and a mobile phone module including a camera. 
   Further embodiments of the invention incorporate a stylus that has an inkjet printhead nib. This embodiment is described in detail in the Applicant&#39;s co-pending application identified by Ser. No. 11/124,167. In the interests of brevity, the disclosure of application Ser. No. 11/124,167 has been incorporated herein by cross reference (see list of cross referenced documents above). 
   The cross referenced application also briefly lists some of the possible applications for the M-Print system. It also discusses embodiments in which the Netpage tag pattern is printed simultaneously with the visible images. 
   Conclusion 
   The present invention has been described with reference to a number of specific embodiments. It will be understood that where the invention is claimed as a method, the invention can also be defined by way of apparatus or system claims, and vice versa. The assignee reserves the right to file further applications claiming these additional aspects of the invention. 
   Furthermore, various combinations of features not yet claimed are also aspects of the invention that the assignee reserves the right to make the subject of future divisional and continuation applications as appropriate.