Patent Publication Number: US-6659581-B2

Title: Integrated programmable fire pulse generator for inkjet printhead assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Non-Provisional Patent Application is a Continuation-in-Part of U.S. Patent Application Ser. No. 09/755,226 “MODULE MANAGER FOR WIDE-ARRAY INKJET PRINTHEAD ASSEMBLY” filed on Jan. 5, 2001, now U.S. Pat No. 6,585,339, which is herein incorporated by reference. 
    
    
     THE FIELD OF THE INVENTION 
     The present invention relates generally to inkjet printheads, and more particularly to generation of fire signals for controlling ejection of ink drops from printheads. 
     BACKGROUND OF THE INVENTION 
     A conventional inkjet printing system includes a printhead, an ink supply which supplies liquid ink to the printhead, and an electronic controller which controls the printhead. The printhead ejects ink drops through a plurality of orifices or nozzles and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other. 
     Typically, the printhead ejects the ink drops through the nozzles by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as thin film resisters. Heating the ink causes the ink to vaporize and be ejected from the nozzles. Typically, for one dot of ink, a remote printhead controller typically located as part of the processing electronics of a printer, controls the timing and activation of an electrical current from a power supply external to the printhead with a fire pulse. The electrical current is passed through a selected thin film resister to heat the ink in a corresponding selected vaporization chamber. 
     In one type of inkjet printing system, printheads receive fire signals containing fire pulses from the electronic controller. In one arrangement, the fire signal is fed directly to the nozzles in the printhead. In another arrangement, the fire signal is latched in the printhead, and the latched version of the fire signal is fed to the nozzles to control the ejection of ink drops from the nozzles. 
     In either of the above two arrangements, the electronic controller of the printer maintains control of all timing related to the fire signal. The timing related to the fire signal primarily refers to the actual width of the fire pulse and the point in time at which the fire pulse occurs. The electronic controller controlling the timing related to the fire signal works well for printheads capable of printing only a single column at a time, because such printheads only need one fire signal to the printhead to control the ejection of ink drops from the printhead. 
     One proposed printhead has the capability of printing multiple columns of the same color or multiple columns of different colors simultaneously. 
     In one arrangement, commonly referred to as a wide-array inkjet printing system, a plurality of individual printheads, also referred to as printhead dies, are mounted on a single carrier. In one proposed arrangement, a wide-array inkjet printing system includes printheads which have the capability of printing multiple columns of the same color or multiple columns of different colors simultaneously. In any of these arrangements, a number of nozzles and, therefore, an overall number of ink drops which can be ejected per second is increased. Since the overall number of drops which can be ejected per second is increased, printing speed can be increased with a wide-array inkjet printing system and/or printheads having the capability of printing multiple columns simultaneously. 
     The energy requirements of different printheads and/or different print columns can possibly require a different fire pulse width for each printhead and/or print column due to processing/manufacturing variability. In this case, the number of fire signals necessary for the inkjet printing system increases significantly. For example, a 4-color integrated printhead requires four fire signals in order to independently control each color. If six of the example 4-color integrated printheads are disposed on a single carrier to form a print bar array in a wide-array inkjet printing system, the number of required fire signals increases to 24. 
     For reasons stated above and for other reasons presented in greater detail in the Description of the Preferred Embodiment section of the present specification, a wide-array inkjet printing system and/or a printhead having the capability of printing multiple columns is desired which minimizes the number of fire signals provided from the electronic controller to the printhead(s). 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides an inkjet printhead including nozzles, firing resisters, and fire pulse generator circuitry. The fire pulse generator circuitry is responsive to a start fire signal to generate a plurality of fire signals. Each fire signal has a series of fire pulses, and the fire pulse generator circuitry generates the fire signals by controlling the initiation and duration of the fire pulses. The fire pulses control timing and activation of electrical current through the firing resisters to thereby control ejection of ink drops from the nozzles. 
     In one embodiment, the fire pulse generator circuitry includes counters. Each counter is responsive to the initiation of a corresponding fire pulse to count to a corresponding count value representing the duration of the corresponding fire pulse. In one embodiment, the fire pulse generator circuitry further includes pulse width registers for holding pulse width values. The counters are each preloaded with a corresponding pulse width value and respond to the initiation of the corresponding fire pulse to count down from the corresponding pulse width value to determine the duration of the corresponding fire pulse. In one embodiment, the fire pulse generator circuitry includes controllers controlling corresponding counters. Each controller provides a corresponding fire pulse and activates a start signal to the corresponding counter to initiate the count. Each counter activates a stop signal to the corresponding controller to terminate the corresponding fire pulse when the count value is reached. 
     In one embodiment, the fire pulse generator circuitry includes a start fire detection circuit receiving the start fire signal and verifying that a valid active start fire signal is received. In one embodiment, the start fire detection circuit receives a clock signal having active transitions and verifies that the valid active start fire signal is received by requiring that the active start fire signal is present for at least two of the active transitions of the clock signal. 
     In one embodiment, an active start fire signal is provided to the fire pulse generator circuitry each time a fire pulse is generated. In another embodiment, an active start fire signal is provided to the fire pulse generator circuitry only at the beginning of a print swath. 
     In one embodiment, the fire pulse generator circuitry also controls dead-time between fire pulses in the series of fire pulses in each fire signal. In one embodiment, the fire pulse generator circuitry includes dead-time counters. Each dead-time counter is responsive to a termination of a corresponding fire pulse to count to a corresponding dead-time count value representing the duration of the dead-time between fire pulses. In one embodiment, the fire pulse generator circuitry further includes dead-time registers for holding dead-time values. The dead-time counters are each preloaded with a corresponding dead-time value and respond to the termination of the corresponding fire pulse to count down from the corresponding dead-time value to determine the dead-time between fire pulses. 
     One aspect of the present invention provides an inkjet printhead assembly including at least one printhead. Each printhead includes nozzles and firing resisters. The inkjet printhead assembly includes fire pulse generator circuitry responsive to a first start fire signal to generate a plurality of fire signals. Each fire signal has a series of fire pulses, and the fire pulse generator circuitry generates the fire signals by controlling the initiation and duration of the fire pulses. The fire pulses control timing and activation of electrical current through the firing resisters to thereby control ejection of ink drops from the nozzles. 
     In one embodiment, the first start fire signal is provided from a printer controller located external from the inkjet printhead assembly. In one embodiment, the inkjet printhead assembly includes a carrier, N printheads disposed on the carrier, and a module manager disposed on the carrier. In one embodiment, the module manager receives a second start fire signal from a printer controller located external from the inkjet printhead assembly and provides the first start fire signal representing the first start signal to each of the N printheads. 
     One aspect of the present invention provides an inkjet printhead assembly including, a carrier, N printheads disposed on the carrier, and a module manager disposed on the carrier. Each printhead includes nozzles and firing resisters. The module manager includes fire pulse generator circuitry responsive to a start fire signal to generate a plurality of fire signals. Each fire signal has a series of fire pulses, and the fire pulse generator circuitry generates the fire signals by controlling the initiation and duration of the fire pulses. The fire pulses control timing and activation of electrical current through the firing resisters to thereby control ejection of ink drops from the nozzles of the printheads. 
     One aspect of the present invention provides an inkjet printing system including a printer controller providing a start fire signal. The inkjet printing system includes an inkjet printhead assembly having at least one printhead and fire pulse generator circuitry. Each printhead includes nozzles and firing resisters. The fire pulse generator circuitry is responsive to the start fire signal to generate a plurality of fire signals. Each fire signal has a series of fire pulses, and the fire pulse generator circuitry generates the fire signals by controlling the initiation and duration of the fire pulses. The fire pulses control timing and activation of electrical current through the firing resisters to thereby control ejection of ink drops from the nozzles. 
     One aspect of the present invention provides a method of inkjet printing including receiving a start fire signal at a printhead assembly, which includes at least one printhead having nozzles and firing resisters. The method includes generating, in response to the start fire signal, a plurality of fire signals, each having a series of fire pulses, by controlling the initiation and duration of the fire pulses internal to the printhead assembly. The method includes controlling timing and activation of electrical current through the firing resisters to thereby control ejection of ink drops from the nozzles based on the fire pulses. 
     An inkjet printhead/printhead assembly according to the present invention can provide different fire pulse widths for different printheads and/or print columns to accommodate the energy requirements of different printheads and/or different print columns resulting from processing/manufacturing variability without increasing the number of fire signals from the printer controller to the printhead/printhead assembly. One embodiment of the fire pulse generator circuitry according to the present invention only requires one start fire conductor between the printer controller and the printhead/printhead assembly. 
     Thus, the printhead/printhead assembly containing fire pulse generator circuitry according to the present invention can significantly reduce the following: the number of fire signal conductive paths to and from the printhead/printhead assembly; the number of drivers in the electronic controller necessary to transmit the fire signals from the electronic controller to the printhead assembly; and the number of pads required on the printhead/printhead assembly to receive the fire signals. Furthermore, in one embodiment having multiple printheads disposed on a carrier to form a printhead assembly and having the fire pulse generator circuitry internal to the printheads, the wiring complexity of the carrier is reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating one embodiment of an inkjet printing system according to the present invention. 
     FIG. 2 is a diagram of one embodiment of an inkjet printhead subassembly or module according to the present invention. 
     FIG. 3 is an enlarged schematic cross-sectional view illustrating portions of a one embodiment of a printhead die in the printing system of FIG.  1 . 
     FIG. 4 is a block diagram illustrating a portion of one embodiment of an inkjet printhead having fire pulse generator circuitry according to the present invention. 
     FIG. 5 is a block diagram illustrating a fire pulse generator employed by the fire pulse generator circuitry of FIG.  4 . 
     FIG. 6 is a block diagram illustrating a portion of one embodiment of an inkjet printhead having an alternative embodiment of fire pulse generator circuitry according to the present invention. 
     FIG. 7 is a block diagram illustrating a portion of an inkjet printhead having fire pulse generator circuitry according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. The inkjet printhead assembly and related components of the present invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     FIG. 1 illustrates one embodiment of an inkjet printing system  10  according to the present invention. Inkjet printing system  10  includes an inkjet printhead assembly  12 , an ink supply assembly  14 , a mounting assembly  16 , a media transport assembly  18 , and an electronic controller  20 . At least one power supply  22  provides power to the various electrical components of inkjet printing system  10 . Inkjet printhead assembly  12  includes at least one printhead or printhead die  40  which ejects drops of ink through a plurality of orifices or nozzles  13  and toward a print medium  19  so as to print onto print medium  19 . Print medium  19  is any type of suitable sheet material, such as paper, card stock, transparencies, Mylar, and the like. Typically, nozzles  13  are arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  13  causes characters, symbols, and/or other graphics or images to be printed upon print medium  19  as inkjet printhead assembly  12  and print medium  19  are moved relative to each other. 
     Ink supply assembly  14  supplies ink to printhead assembly  12  and includes a reservoir  15  for storing ink. As such, ink flows from reservoir  15  to inkjet printhead assembly  12 . Ink supply assembly  14  and inkjet printhead assembly  12  can form either a one-way ink delivery system or a recirculating ink delivery system. In a one-way ink delivery system, substantially all of the ink supplied to inkjet printhead assembly  12  is consumed during printing. In a recirculating ink delivery system, however, only a portion of the ink supplied to printhead assembly  12  is consumed during printing. As such, ink not consumed during printing is returned to ink supply assembly  14 . 
     In one embodiment, inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet cartridge or pen. In another embodiment, ink supply assembly  14  is separate from inkjet printhead assembly  12  and supplies ink to inkjet printhead assembly  12  through an interface connection, such as a supply tube. In either embodiment, reservoir  15  of ink supply assembly  14  may be removed, replaced, and/or refilled. In one embodiment, where inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet cartridge, reservoir  15  includes a local reservoir located within the cartridge as well as a larger reservoir located separately from the cartridge. As such, the separate, larger reservoir serves to refill the local reservoir. Accordingly, the separate, larger reservoir and/or the local reservoir may be removed, replaced, and/or refilled. 
     Mounting assembly  16  positions inkjet printhead assembly  12  relative to media transport assembly  18  and media transport assembly  18  positions print medium  19  relative to inkjet printhead assembly  12 . Thus, a print zone  17  is defined adjacent to nozzles  13  in an area between inkjet printhead assembly  12  and print medium  19 . In one embodiment, inkjet printhead assembly  12  is a scanning type printhead assembly. As such, mounting assembly  16  includes a carriage for moving inkjet printhead assembly  12  relative to media transport assembly  18  to scan print medium  19 . In another embodiment, inkjet printhead assembly  12  is a non-scanning type printhead assembly. As such, mounting assembly  16  fixes inkjet printhead assembly  12  at a prescribed position relative to media transport assembly  18 . Thus, media transport assembly  18  positions print medium  19  relative to inkjet printhead assembly  12 . 
     Electronic controller or printer controller  20  typically includes a processor, firmware, and other printer electronics for communicating with and controlling inkjet printhead assembly  12 , mounting assembly  16 , and media transport assembly  18 . Electronic controller  20  receives data  21  from a host system, such as a computer, and includes memory for temporarily storing data  21 . Typically, data  21  is sent to inkjet printing system  10  along an electronic, infrared, optical, or other information transfer path. Data  21  represents, for example, a document and/or file to be printed. As such, data  21  forms a print job for inkjet printing system  10  and includes one or more print job commands and/or command parameters. 
     In one embodiment, logic and drive circuitry are incorporated in a module manager integrated circuit (IC)  50  located on inkjet printhead assembly  12 . Module manger IC  50  is similar to the module manager IC discussed in the above incorporated parent patent application entitled “MODULE MANAGER FOR WIDE-ARRAY INKJET PRINTHEAD ASSEMBLY.” Electronic controller  20  and module manager IC  50  operate together to control inkjet printhead assembly  12  for ejection of ink drops from nozzles  13 . As such, electronic controller  20  and module manager IC  50  define a pattern of ejected ink drops which form characters, symbols, and/or other graphics or images on print medium  19 . The pattern of ejected ink drops, is determined by the print job commands and/or command parameters. 
     In one embodiment, inkjet printhead assembly  12  is a wide-array or multi-head printhead assembly. In one embodiment, inkjet printhead assembly  12  includes a carrier  30 , which carries printhead dies  40  and module manager IC  50 . In one embodiment carrier  30  provides electrical communication between printhead dies  40 , module manager IC  50 , and electronic controller  20 , and fluidic communication between printhead dies  40  and ink supply assembly  14 . 
     In one embodiment, printhead dies  40  are spaced apart and staggered such that printhead dies  40  in one row overlap at least one printhead die  40  in another row. Thus, inkjet printhead assembly  12  may span a nominal page width or a width shorter or longer than nominal page width. In one embodiment, a plurality of inkjet printhead sub-assemblies or modules  12 ′ (illustrated in FIG. 2) form one inkjet printhead assembly  12 . The inkjet printhead modules  12 ′ are substantially similar to the above described printhead assembly  12  and each have a carrier  30  which carries a plurality of printhead dies  40  and a module manager IC  50 . In one embodiment, the printhead assembly  12  is formed of multiple inkjet printhead modules  12 ′ which are mounted in an end-to-end manner and each carrier  30  has a staggered or stair-step profile. As a result, at least one printhead die  40  of one inkjet printhead module  12 ′ overlaps at least one printhead die  40  of an adjacent inkjet printhead module  12 ′. 
     A portion of one embodiment of a printhead die  40  is illustrated schematically in FIG.  3 . Printhead die  40  includes an array of printing or drop ejecting elements  42 . Printing elements  42  are formed on a substrate  44  which has an ink feed slot  441  formed therein. As such, ink feed slot  441  provides a supply of liquid ink to printing elements  42 . Each printing element  42  includes a thin-film structure  46 , an orifice layer  47 , and a firing resistor  48 . Thin-film structure  46  has an ink feed channel  461  formed therein which communicates with ink feed slot  441  of substrate  44 . Orifice layer  47  has a front face  471  and a nozzle opening  472  formed in front face  471 . Orifice layer  47  also has a nozzle chamber  473  formed therein which communicates with nozzle opening  472  and ink feed channel  461  of thin-film structure  46 . Firing resistor  48  is positioned within nozzle chamber  473  and includes leads  481  which electrically couple firing resistor  48  to a drive signal and ground. 
     During printing, ink flows from ink feed slot  441  to nozzle chamber  473  via ink feed channel  461 . Nozzle opening  472  is operatively associated with firing resistor  48  such that droplets of ink within nozzle chamber  473  are ejected through nozzle opening  472  (e.g., normal to the plane of firing resistor  48 ) and toward a print medium upon energization of firing resistor  48 . 
     Example embodiments of printhead dies  40  include a thermal printhead, a piezoelectric printhead, a flex-tensional printhead, or any other type of inkjet ejection device known in the art. In one embodiment, printhead dies  40  are fully integrated thermal inkjet printheads. As such, substrate  44  is formed, for example, of silicon, glass, or a stable polymer and thin-film structure  46  is formed by one or more passivation or insulation layers of silicon dioxide, silicon carbide, silicon nitride, tantalum, poly-silicon glass, or other suitable material. Thin-film structure  46  also includes a conductive layer which defines firing resistor  48  and leads  481 . The conductive layer is formed, for example, by aluminum, gold, tantalum, tantalum-aluminum, or other metal or metal alloy. 
     In one embodiment, at least one printhead  40  of printhead assembly  12  is implemented as a printhead having the capability of printing multiple columns of the same color or multiple columns of different colors simultaneously. 
     Printhead assembly  12  can include any suitable number (N) of printheads  40 , where N is at least one. Before a print operation can be performed, data must be sent to printhead  40 . Data includes, for example, print data and non-print data for printhead  40 . Print data includes, for example, nozzle data containing pixel information, such as bitmap print data. Non-print data includes, for example, command/status (CS) data, clock data, and/or synchronization data. Status data of CS data includes, for example, printhead temperature or position, printhead resolution, and/or error notification. 
     A portion of one embodiment of a printhead  40  is illustrated generally in FIG. 4 in block diagram form. As discussed in the Background of the Invention section of the present specification, conventional inkjet printing systems typically employ an electronic controller remote from the printhead to control the timing and activation of an electrical current from a power supply external to the printhead with a fire signal to thereby control the ejection of ink drops from the printhead. In the conventional inkjet printing system, printheads receive fire signals containing fire pulses from the electronic controller. By contrast, printhead  40  generally illustrated in FIG. 4, includes integrated programmable fire pulse generators for generating fire signals containing fire pulses for controlling ejection of ink drops from printhead  40 . 
     Fire pulse generator circuitry  100  includes a start_fire detection circuit  102  which receives a start_fire signal on a line  104  from electronic controller  20  or module manager IC  50 . Start_fire detection circuit  102  also receives a clock signal on line  106 . Start_fire detection circuit  102  verifies when a valid active start_fire signal is received on line  104 . Start_fire detection circuit  102  prevents a spurious transition on the start_fire signal on line  104  from causing a fire pulse to be generated at an improper or undesired time. 
     In one embodiment, start_fire detection circuit  102  verifies that a valid active start_fire signal is received on line  104  by requiring that the active start_fire signal on line  104  be present for two active transitions of the clock signal on line  106  to be considered a valid active start_fire signal. There are, however, many suitable validations methods which can be employed by start_fire detection circuit  102  to verify that the start_fire signal on line  104  indicates a valid active start_fire signal. 
     In response to the start_fire detection circuit  102  validating that the active start_fire signal on line  104  is properly received, the start_fire detection circuit  102  activates a begin_pulse signal on a line  108 . 
     Fire pulse generator circuitry  100  includes N pulse width registers  110   a ,  110   b , . . . ,  110   n . Pulse width registers  110   a - 110   n  receive data on data_bus  112  and addresses from address_bus  114 . The clock on line  106  is also provided to pulse width registers  110   a - 110   n . Pulse width registers  110   a - 110   n  store pulse width values which are employed to determine the widths of the fire pulses provided from fire pulse generator circuitry  100 . Pulse width registers  110   a - 110   n  respectively provide pulse counts 1, 2, . . . , N on busses  116   a ,  116   b , . . . ,  116   n,  which represent the corresponding pulse width values stored in pulse width registers  110   a - 110   n . Each pulse width register  110   a - 110   n  stores an appropriate number of bits in the pulse width value to properly encode the desired width of the corresponding fire pulse from fire pulse generator circuitry  100 . 
     Fire pulse generator circuitry  100  includes N fire pulse generators  118   a ,  118   b , . . . ,  118   n  corresponding to pulse width registers  110   a - 110   n  respectively. Fire pulse generators  118   a - 118   n  all receive the begin_pulse signal on line  108  from start_fire detection circuit  102  and the clock signal on line  106 . In addition, fire pulse generators  118   a - 118   n  receive the pulse counts 1-N on busses  116   a - 116   n  respectively. Fire pulse generators  118   a - 118   n  respectively provide the fire signals fire_pulse — 1, fire_pulse — 2, . . . , fire_pulse_N respectively on lines  120   a ,  120   b , . . . ,  120   n.    
     In one embodiment, each fire pulse generator  118   a - 118   n  includes a counter which is controlled by the corresponding pulse count signal on the corresponding bus  116 . In one example embodiment, fire pulse generators  118   a - 118   n  respectively include binary countdown counters  122   a ,  122   b , . . . ,  122   n . In this example embodiment, the respective binary countdown counter  122  is preloaded with the pulse width value stored in the corresponding pulse width register  110  and provided as the pulse count signal on the corresponding bus  116 . 
     In one embodiment, the pulse width value stored in each pulse width register  110  is given by the following Equation I. 
     Equation I 
     
       
         (Pulse Width Value)=(Desired Pulse Width)×(Clock Frequency)  
       
     
     Electronic controller  20  of inkjet printing system  10  can access pulse width registers  110   a - 110   n  in the same manner that electronic controller  20  accesses the other registers in printhead  40  via data_bus  112  and address bus  114 . Thus, no extra control circuitry is required to implement the pulse width registers  110   a - 110   n . In one embodiment, command data from electronic controller  20  which is independent of nozzle data is provided to and status data read from printhead  40  over a serial bi-directional non-print data serial bus  68 . In another embodiment, module manger IC  50  communicates with electronic controller  20  over serial bi-directional non-print data serial bus  68 , and module manager IC  50  writes command data to and reads status data from printheads  40  over serial bi-directional CS data line  78 . In either embodiment, electronic controller  20  can access pulse width registers  110   a - 110   n  via bi-directional non-print data serial bus  68  which communicates serial data to and from data_bus  112  and address_bus  114 . 
     One embodiment of a fire pulse generator  118  is illustrated in block diagram form in FIG.  5 . Fire pulse generator  118  includes binary countdown counter  122  and a controller  124 . Countdown counter  122  receives the pulse count from bus  116  which provides the pulse width value from the corresponding pulse width register  110  for preloading countdown counter  122 . 
     Controller  124  receives the begin_pulse signal on line  108  and the clock signal on line  106 . The clock signal on line  106  is also provided to countdown counter  122 . Controller  124  provides the fire_pulse signal on line  120 . Controller  124  also provides a start signal to countdown counter  122  on line  126 . Countdown counter  122  correspondingly provides a stop signal on a line  128  to controller  124 . The fire_pulse signal on line  120  is provided to control the ejection of ink drops from nozzles of printhead  40 . 
     In one embodiment, controller  124  includes state machines which control the generation of a properly timed fire_pulse signal on line  120 . Controller  124  accepts the active begin_pulse signal from the start_fire detection circuit  102  and accordingly initiates a fire_pulse on line  120 . When controller  124  initiates the fire_pulse on line  120 , controller  124  also activates the start signal on line  126  to initiate a timing function of countdown counter  122  for timing the duration of the fire_pulse on line  120 . Controller  124  controls the preloading of countdown counter  122  with the pulse count on bus  116 , which represents the pulse width value from pulse width register  110 . Controller  124  terminates the fire_pulse on line  120  in response to receiving an activated stop signal on line  128  from countdown counter  122 . 
     Countdown counter  122  functions as a timing circuit to ensure that the fire_pulse generated on line  120  by controller  124  is of a proper duration. One embodiment of countdown counter  122  is a binary countdown counter which is preloaded with the pulse width value from pulse width register  110 . Upon receipt of an activated start signal on line  126  from controller  124 , countdown counter  122  begins to countdown. In one example embodiment, when the count value stored in countdown counter  122  reaches zero, countdown counter  122  activates the stop signal on line  128 , and controller  124  correspondingly responds to the activated stop signal to terminate the fire_pulse on line  120 . 
     In the above-described embodiments illustrated in FIGS. 4 and 5, electronic controller  20  or module manager IC  50  is required to activate the start_fire signal each time a corresponding fire_pulse is generated by the fire pulse generators  118 . Accordingly, in the above described embodiments, electronic controller  20  and/or module manager  50  is required to maintain control of when the fire_pulses actually occur. 
     A portion of an alternative embodiment printhead  40 ′ having alternative embodiment fire_pulse generator circuitry  200  is illustrated in block diagram form in FIG.  6 . Fire pulse generator circuitry  200  automatically generates fire_pulses having the proper duration and also automatically generates the proper dead time between fire pulses in a series of fire pulses in each fire signal. 
     Fire pulse generator circuitry  200  includes a start_fire detection circuit  202  receiving a start_fire signal on a line  204  and a clock signal on a line  206 . Start_fire detection circuit  202  functions substantially similar to the start_fire detection circuit  102  of fire pulse generator circuitry  100  and accordingly activates a begin_pulse signal on a line  208  after verifying that a valid active start_fire signal on line  204  has been provided from electronic controller  20  or module manager IC  50 . However, the start_fire signal on line  204  need only be activated by electronic controller  20  or module manager IC  50  at the beginning of a print swath rather than maintaining control of when each of the fire_pulses actually occur. Thus, the begin_pulse signal is also only activated in response to a valid activated start_fire signal at the beginning of a print swath. 
     Fire pulse generator circuitry  200  includes pulse width registers  210   a - 210   n  receiving data on data_bus  212 , addresses on address_bus  214 , and the clock on line  206 . The pulse width registers  210   a - 210   n  hold pulse width values corresponding to the desired pulse widths of the fire_pulses generated by fire pulse generator circuitry  200 . The pulse width registers  210   a - 210   n  function substantially similar to the pulse width registers  110   a - 110   n  of fire pulse generator circuitry  100  and accordingly provide pulse count signals  1 -N on corresponding busses  216   a - 216   n , which represent the pulse width values. 
     In addition to the pulse width registers  210   a - 210   n , fire pulse generator circuitry  200  includes N dead-time registers  230   a ,  230   b , . . . ,  230   n  which also receive data from data_bus  212 , addresses from address_bus  214 , and the clock on line  206 . The dead-time registers  230   a - 230   n  store N dead-time values which represent proper dead times between fire_pulses. Dead-time registers  230   a - 230   n  accordingly provide dead-time counts on busses  232   a ,  232   b , . . . ,  230   n , which represent the dead-time values. 
     Fire pulse generator circuitry  200  also includes fire pulse generators  218   a ,  218   b , . . . ,  218   n . Fire pulse generators  218   a - 218   n  include corresponding binary countdown counters  222   a ,  222   b , . . . ,  222   n , which are preloaded with the pulse width values represented by the pulse counts provided from pulse width registers  210   a - 210   n  on busses  216   a - 216   n . Countdown counters  222   a - 222   n  are substantially similar to countdown counters  122   a - 122   n  of fire pulse generators  118   a - 118   n . Fire pulse generators  218   a - 218   n  also include corresponding dead-time binary countdown counters  234   a ,  234   b , . . . ,  234   n . Dead-time countdown counters  234   a - 234   n  are preloaded with the dead-time values from dead-time registers  230   a - 230   n  provided as the dead-time counts on busses  232   a - 232   n.    
     Fire pulse generators  218   a - 218   n  each include a controller  224  which functions similar to controller  124  of fire pulse generator  118  in controlling countdown counters  222   a - 222   n . However, controller  224  also controls the dead-time countdown counters  234   a - 234   n . Controller  224  accordingly provides the proper width of the fire_pulses based on the timing function provided by countdown counter  222 . In addition, controller  224  provides the proper dead time between fire_pulses based on the timing function provided by dead-time countdown counter  234 . In one embodiment, controller  224  includes state machines which respond to countdown counter  222  and dead-time countdown counter  234  to generate fire_pulses of proper duration with proper dead time between fire pulses, which are provided as fire_pulse signals fire_pulse — 1, fire_pulse — 2, . . . , fire_pulse_N on lines  220   a ,  220   b , . . . ,  220   n  to control the ejection of ink drops from the printhead nozzles. 
     In each fire pulse generator  218 , the dead-time countdown counter  234  is reset by controller  224  at the end of each fire_pulse generated by the fire pulse generator  218  and is initiated at this time to begin counting down from the preloaded dead-time value provided from the corresponding dead-time register  230  to automatically generate the proper dead time between fire pulses. In this way, fire pulse generator circuitry  200  maintains control of when the individual fire pulses from fire pulse generators  218  actually occur, and fire pulse generator circuitry  200  only needs to be initiated with a start_fire signal activation from electronic controller  20  or module manager IC  50  at the beginning of a print swath. 
     A portion of one embodiment of an inkjet printhead assembly  12  is illustrated generally in FIG.  7 . Inkjet printhead assembly  12  includes complex analog and digital electronic components. Thus, inkjet printhead assembly  12  includes printhead power supplies for providing power to the electronic components within printhead assembly  12 . For example, a Vpp power supply  52  and corresponding power ground  54  supply power to the firing resisters in printheads  40 . An example 5-volt analog power supply  56  and corresponding analog ground  58  supply power to the analog electronic components in printhead assembly  12 . An example 5-volt logic supply  60  and a corresponding logic ground  62  supply power to logic devices requiring a 5-volt logic power source. A 3.3-volt logic power supply  64  and the logic ground  62  supply power to logic components requiring a 3.3-volt logic power source, such as module manager  50 . In one embodiment, module manager  50  is an application specific integrated circuit (ASIC) requiring a 3.3-volt logic power source. 
     In the example embodiment illustrated in FIG. 7, printhead assembly  12  includes eight printheads  40 . Printhead assembly  12  can include any suitable number (N) of printheads. Before a print operation can be performed, data must be sent to printheads  40 . Data includes, for example, print data and non-print data for printheads  40 . Print data includes, for example, nozzle data containing pixel information, such as bitmap print data. Non-print data includes, for example, command/status (CS) data, clock data, and/or synchronization data. Status data of CS data includes, for example, printhead temperature or position, printhead resolution, and/or error notification. 
     Module manager IC  50  according to the present invention receives data from electronic controller  20  and provides both print data and non-print data to the printheads  40 . For each printing operation, electronic controller sends nozzle data to module manager IC  50  on a print data line  66  in a serial format. The nozzle data provided on print data line  66  may be divided into two or more sections, such as even and odd nozzle data. In the example embodiment illustrated in FIG. 7, serial print data is received on print data line  66  which is  6  bits wide. The print data line  66  can be any suitable number of bits wide. 
     Independent of nozzle data, command data from electronic controller  20  may be provided to and status data read from printhead assembly  12  over a serial bi-directional non-print data serial bus  68 . 
     A clock signal from electronic controller  20  is provided to module manager IC  50  on a clock line  70 . A busy signal is provided from module manager IC  50  to electronic controller  20  on a line  72 . 
     Module manager IC  50  receives the print data on line  66  and distributes the print data to the appropriate printhead  40  via data line  74 . In the example embodiment illustrated in FIG. 7, data line  74  is 32 bits wide to provide four bits of serial data to each of the eight printheads  40 . Data clock signals based on the input clock received on line  70  are provided on clock line  76  to clock the serial data from data line  74  into the printheads  40 . In the example embodiment illustrated in FIG. 7, clock line  76  is eight bits wide to provide clock signals to each of the eight printheads  40 . 
     Module manager IC  50  writes command data to and reads status data from printheads  40  over serial bi-directional CS data line  78 . A CS clock is provided on CS clock line  80  to clock the CS data from CS data line  78  to printheads  40  and to module manager  50 . 
     In the example embodiment of inkjet printhead assembly  12  illustrated in FIG. 7, the number of conductive paths in the print data interconnect between electronic controller  20  and inkjet printhead assembly  12  is significantly reduced, because an example module manager IC (e.g., ASIC)  50  is capable of much faster data rates than data rates provided by current printheads. For one example printhead design and example module manager ASIC  50  design, the print data interconnect is reduced from 32 pins to six lines to achieve the same printing speed, such as in the example embodiment of inkjet printhead assembly  12  illustrated in FIG.  7 . This reduction in the number of conductive paths in the print data interconnect significantly reduces costs and improves reliability of the printhead assembly and the printing system. 
     In addition, module manager IC  50  can provide certain functions that can be shared across all the printheads  40 . In this embodiment, the printhead  40  can be designed without certain functions, such as memory and/or processor intensive functions, which are instead performed in module manager IC  50 . In addition, functions performed by module manager IC  50  are more easily updated during testing, prototyping, and later product revisions than functions performed in printheads  40 . 
     Moreover, certain functions typically performed by electronic controller  20  can be incorporated into module manager IC  50 . For example, one embodiment of module manager IC  50  monitors the relative status of the multiple printheads  40  disposed on carrier  30 , and controls the printheads  40  relative to each other, which otherwise could only be monitored/controlled relative to each other off the carrier with the electronic controller  20 . 
     In one embodiment, module manager IC  50  permits standalone printheads to operate in a multi-printhead printhead assembly  12  without modification. A standalone printhead is a printhead which is capable of being independently coupled directly to an electronic controller. One example embodiment of printhead assembly  12  includes standalone printheads  40  which are directly coupled to module manger IC  50 . 
     As illustrated in FIG. 7, one embodiment of module manager IC  50  includes fire pulse generator circuitry, such as fire pulse generator circuitry  100  described above and illustrated in FIGS. 4 and 5 or fire pulse generator circuitry  200  described above and illustrated in FIG.  6 . The fire pulse generator circuitry in module manager IC  50  operates substantially similar to the fire pulse generator circuitry in the printhead  40  illustrated in FIG. 4 or the printhead  40 ′ illustrated in FIG. 6, except that the fire_pulses are no longer generated in the printheads  40 , and therefore, need to be provided to the printheads  40  on lines  320  (shown in FIG.  7 ). 
     Thus, fire pulse generator circuitry  100 / 200  receives the start_fire signal on line  104 / 204  and verifies when a valid active start_fire signal is received. Fire pulse generator circuitry  100 / 200  responds to the validated active start_fire signal to initiate fire_pulses on lines  320  of proper duration. In addition, as described above, in the fire pulse generator circuitry  200  embodiment, the dead_time between fire_pulses is also provided by fire pulse generator circuitry  200 . 
     In the printhead embodiments illustrated in FIGS. 4-6, the fire pulse generator circuitry is contained within the printhead which enables the printhead to automatically generate fire pulses of proper duration. In the embodiment illustrated in FIG. 7, the printhead assembly  12  via module manager IC  50  automatically generates the fire pulses of proper duration. In any of these embodiments, electronic controller  20  of inkjet printing system  10  according to the present invention does not need to generate the individual fire pulses. In addition, in the alternative embodiment of fire pulse generator circuitry  200  illustrated in FIG. 6, the proper dead time between fire pulses is generated in the printhead  40  or module manager IC  50  so that electronic controller  20  of the inkjet printing system according to the present invention does not need to maintain control of when the fire pulses actually occur. 
     As discussed in the Background of the Invention section, the energy requirements of different printheads and/or different print columns can possibly require a different fire pulse width for each printhead and/or print column due to processing/manufacturing variability. In this case, the number of fire signals necessary for the inkjet printing system increases significantly. In such a system, the fire pulse generator circuitry according to the present invention, such as fire pulse generator circuitry  100  or  200 , only requires one start_fire conductor between electronic controller  20  and the printhead/printhead assembly. Thus, the printhead/printhead assembly containing fire pulse generator circuitry according to the present invention can significantly reduce the number of fire signal conductive paths to and from the printhead/printhead assembly. 
     In an example printhead assembly having eight 4-slot color printheads on a common carrier, the number of required fire signals is reduced from 32 to 1 with the fire pulse generator circuitry according to the present invention. This not only significantly reduces the number of fire signal conductors necessary in the electrical interconnect between the electronic controller and the printhead assembly, but also significantly reduces the number of drivers in the electronic controller necessary to transmit the fire signals from the electronic controller to the printhead assembly. In addition, the fire pulse generator circuitry according to the present invention also significantly reduces the number of pads required on the printhead/printhead assembly to receive the fire signals. The reduced number of fire signal conductors in the electrical interconnect between the electronic controller and the printhead assembly correspondingly reduces the amount of undesirable electromagnetic interference (EMI) conducted through the fire signal conductors. Moreover, in the embodiment where there are multiple printheads mounted on a carrier to form a printhead assembly, and the fire pulse generator circuitry is internal to the printheads, the wiring complexity of the carrier is reduced. 
     Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the chemical, mechanical, electromechanical, electrical, and computer arts will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.