Abstract:
A manner of reducing the power consumption is utilized in a tablet terminal equipped with a digitizer for inputting with an electronic pen. When another tablet terminal or a smartphone approaches the tablet terminal, each digitizer detects input. When the digitizer detects the input, it is determined whether the input is electronic pen input from the electronic pen or proximity input caused by the proximity of the other tablet terminal or the smartphone. In the case of electronic pen input, coordinate information is transferred to a system, while in the case of proximity input, the system takes an action such as shifting a tablet terminal to a sleep state.

Description:
FIELD 
     The disclosed embodiments relate to techniques for detecting input to a coordinate input device for inputting with an electronic pen, and for detecting input attributed to any factor other than an operation of the electronic pen to control the operation of an electronic device. 
     BACKGROUND 
     Electronic devices such as tablet terminals, smartphones, and certain types of laptop personal computers (laptop PC) are equipped with a touch screen as an input unit made up by combining a touch panel and a display. Since control of the screen is operated with a finger, the touch screen can be operated more easily and intuitively than the case where a mouse cursor is operated using a mouse or a track point. 
     Although these electronic devices are generally equipped with a single touch screen, dual screen computers equipped with two touch screens are beginning to appear. There is also a digitizer display made up by combining a digitizer and a display as an input unit for a computer. Since the screen of the digitizer display is operated with an electronic pen, it is convenient to point out a small object. When the digitizer is embedded in the touch screen, since the input method of either a finger or an electronic pen can be selected depending on the work, the operability is improved. 
     SUMMARY 
     A first aspect of the disclosed embodiments is implemented in an electronic device equipped with a coordinate input device for inputting with an electronic pen. A reference pattern for determining the type of input is prepared, and when input coordinates to the coordinate input device are detected, the reference pattern and the input coordinates are compared. When it is determined that the input of the input coordinates is generated by an operation of the electronic pen, coordinate information is transferred to a system, while when it is determined that the input is generated by a cause other than the operation of the electronic pen, a control event is transferred to the system. 
     The cause other than the operation of the electronic pen is caused by the proximity of an object that emits an electromagnetic wave actively or passively. Specifically, it is a case where another electronic device equipped with a coordinate input device emitting an electromagnetic wave approaches the electronic device, or a case where a coil passively emitting an electromagnetic wave approaches the electronic device. The electronic device can be a tablet terminal or a smartphone. The electronic device can be a dual screen computer coupled with another electronic device equipped with a coordinate input device openably/closably, or openably/closably and attachably/detachably. 
     The coordinate input device can be an electromagnetic induction-type digitizer that operates in a transmission mode and a reception mode. The digitizer may be combined with a display to form a touch screen. The reference pattern can be a pattern of temporal and spatial generation of the detected coordinates. The reference pattern may include pen pressure information on the detected coordinates. The reference pattern can be either a pattern generated by an operation of the electronic pen or a pattern generated by a cause other than the operation of the electronic pen. 
     When an electromagnetic wave generated by a cause other than the operation of the electronic pen is detected, the electronic device can determine a given coordinate domain in which input is generated, though the detected coordinate information does not reflect a user&#39;s intention. Therefore, if the user selects a coordinate domain in which proximity input is generated, the electronic device can generate a different control event based on the coordinate domain determined. The control event can be an event for shifting the electronic device to a sleep state, performing data synchronization with another electronic device, or transferring data to another electronic device. 
     A second aspect of the disclosed embodiments is implemented in a computer system configured to include a first coordinate input device for inputting with an electronic pen, and a second coordinate input device for inputting with an electronic pen and allowing the first coordinate input device to approach. A reference pattern for determining the type of input is prepared, and input coordinates to the first coordinate input device or the second coordinate input device are detected. When it is determined that the input of the input coordinates is generated by an operation of the electronic pen, coordinate information is transferred to the system. When it is determined that the input of the input coordinates is generated by a cause other than the operation of the electronic pen, a control event is transferred to the system. 
     The computer system can be a dual screen computer in which a tablet terminal equipped with a first coordinate input device and a tablet terminal equipped with a second coordinate input device are coupled openably/closably, or openably/closably and attachably/detachably. In this case, the operation of the computer system can be stopped according to a control event generated when being closed. 
     A third aspect of the disclosed embodiments is implemented in an electronic device equipped with a second coordinate input device for inputting with an electronic pen and allowing a first coordinate input device for inputting with an electronic pen to approach. A reference pattern for determining the type of input is prepared, and input coordinates to the second coordinate input device are detected. When it is determined that the input of the input coordinates is generated by an operation of the electronic pen, coordinate information is transferred to a system, while when it is determined that the input of the input coordinates is generated by the proximity of the first coordinate input device, a control event is transferred to the system. 
     A first coordinate domain and a second coordinate domain can be defined for the second coordinate input device to determine in which of the first coordinate domain and the second coordinate domain the input coordinates are generated. In this case, when it is determined that the input of the input coordinates is generated in the first coordinate domain, a first control event can be transferred, while when it is determined that the input of the input coordinates is generated in the second coordinate domain, a second control event can be transferred. The electronic device shifted to a power-saving state can detect the proximity of the first coordinate input device to the second coordinate input device so as to wake up. The first coordinate input device can be mounted in a smartphone. The disclosed embodiments can also be implemented as a method of reducing the power consumption of an electronic device equipped with a coordinate input device for inputting with an electronic pen, preventing erroneous input, or transferring data. 
     According to the disclosed embodiments, there can be provided a method of controlling the operation of an electronic device equipped with a coordinate input device for inputting with an electronic pen. According to the disclosed embodiments, there can also be provided a method of reducing the power consumption of an electronic device equipped with a coordinate input device for inputting with an electronic pen. According to the disclosed embodiments, there can further be provided a method of preventing erroneous input of an electronic device equipped with a coordinate input device for inputting with an electronic pen. Further, according to the disclosed embodiments, there can be provided a method of synchronize or transfer data between an electronic device equipped with a coordinate input device for inputting with an electronic pen and another electronic device. Further, according to the disclosed embodiments, there can be provided a computer program and an electronic device for implementing such a method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the application will be readily understood, a more particular description of the application briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the application and are not therefore to be considered to be limiting of its scope, the application will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1A-1C  are perspective views illustrating one aspect of a computer system that configures a dual digitizer system; 
         FIG. 2  is a functional block diagram illustrating an example of the configuration of a dual screen computer; 
         FIGS. 3A and 3B  are perspective views illustrating the structures of touch screens  37  and  33 ; 
         FIG. 4  is a functional block diagram illustrating an example of the configuration of a digitizer panel  107 ; 
         FIG. 5  is a functional block diagram illustrating an example of the configuration of a digitizer panel  207 ; 
         FIG. 6  is a flowchart diagram illustrating an operation procedure when the dual screen computer  30  is closed; 
         FIG. 7  is a block diagram illustrating a state of synchronizing or transferring data between a tablet terminal  51  and a smartphone  61 ; 
         FIG. 8  is a flowchart diagram illustrating an operation procedure when data is transferred between the tablet terminal  51  and the smartphone  61 ; and 
         FIG. 9  is a block diagram illustrating a cover with coils attached thereto. 
     
    
    
     DETAILED DESCRIPTION 
     In this specification, an input display device made up by combining a display and a digitizer to input only with an electronic pen, and an input display device made up by combining a display, a digitizer, and a touch panel to enable input both with a finger and an electronic pen are simply called touch screens unless otherwise particularly noted. Like a laptop PC called a so-called a clamshell type, a certain type of dual screen computer is so configured that two tablet terminals, each with a touch screen mounted thereon, are coupled openably/closably with hinges. 
     Another type of dual screen computer is so configured that one tablet terminal is attached to the other tablet terminal as a base openably/closably and attachably/detachably. In this case, a touch screen mounted on the attached/detached tablet terminal may be of a different type from that of a touch screen mounted on the tablet terminal as the base. Like the laptop PC, the dual screen computer is also put into a state of closing the two tablet terminals to make it convenient for a user to carry around or store when not in use. 
     At this time, a magnet type or mechanical type of lid sensor can be operated without performing a special operation in the case of a laptop PC to shift the system to a sleep state. In the case of a single tablet terminal, when a screen is covered with a cover, sensor magnets embedded in the cover and a main body generate a sleep event to shift the system to the sleep state. However, in the case of a dual screen computer, such a cover cannot be attached. 
     Further, a sensor magnet may not be mounted in the tablet terminal from the standpoint of the space and the cost. In a detachable dual screen computer, various types of tablet terminals may be attached. When a sensor magnet is mounted in the tablet terminal as the base, the mounting position of the sensor magnet in each tablet terminal to be attached to the base is fixed, and this limits the degree of freedom of the design. Further, in the detachable dual screen computer, a tablet terminal with no sensor magnet mounted therein may be attached. 
     A housing may be closed in a manner such that two touch screens face each other when a dual screen computer is running. In the case of an electromagnetic induction-type digitizer as shown in Patent Document 1, electromagnetic waves emitted from each other interfere with each other, resulting in pseudo input to each other&#39;s tablet terminals. For example, if one tablet terminal is displaying an icon on a home screen and the other tablet terminal is displaying a software keyboard, a state similar to a touch on the icon at random or key input may occur, and this may cause the runaway of the system. 
       FIG. 1  is a diagram illustrating one aspect of a computer system that configures a dual digitizer system. The dual digitizer system is a computer system configured to include two digitizers that potentially approach each other. Each digitizer may be a component of a touch screen.  FIG. 1A  shows an example in which the dual digitizer system is realized by an integrated-type dual screen computer  10 . 
     The dual screen computer  10  is so configured that a display-side housing  11  with a touch screen  13  mounted thereon and a base-side housing  15  with a touch screen  17  mounted thereon are coupled openably/closably with hinges  19   a  and  19   b . The dual screen computer  10  displays a software keyboard on the touch screen  17  and an icon or an application screen on the touch screen  13  so that it can be used like a laptop PC. 
     The dual screen computer  10  is also configured such that, when the display-side housing  11  is opened to 180 degrees, screens displayed on the touch screen  13  and the touch screen  17  can be used as one screen and operated with a finger or an electronic pen.  FIG. 1B  shows an example in which the dual digitizer system is realized by a detachable dual screen computer  30 . 
     The dual screen computer  30  is so configured that a tablet terminal  35  with a touch screen  37  mounted thereon and a tablet terminal  31  with a touch screen  33  mounted thereon will be coupled attachably/detachably with attaching/detaching mechanisms  39   a  and  39   b . The tablet terminal  31  and the tablet terminal  35  are connected through a cable or radio interface when they are coupled. In a separated state, the tablet terminal  31  and the tablet terminal  35  function as tablet terminals, respectively, while in a coupled state, the tablet terminal  31  and the tablet terminal  35  cooperate with each other to configure an integrated computer system. Tablet terminals from various manufacturers and of various types can be attached to the attaching/detaching mechanisms  39   a  and  39   b . Further, the touch screen  33  and the touch screen  37  can be closed to face each other in the coupled state in order to make it convenient for a user to carry around or store. 
       FIG. 1C  shows an example in which the dual digitizer system is realized by a tablet terminal  51  with a touch screen  53  mounted thereon and a smartphone  61  with a touch screen  63  mounted thereon. The tablet terminal  51  and the smartphone  61  operate independently of each other individually, and when approaching each other to overlap the touch screen  53  and the touch screen  63 , the tablet terminal  51  and the smartphone  61  configure the dual digitizer system to perform a unique operation. 
       FIG. 2  is a functional block diagram illustrating an example of the configuration of the dual screen computer  30  shown in  FIG. 1B . Although the configurations of the tablet terminals  35  and  31  may be different, the description will be made as the same configuration here. Each of the tablet terminals  35  and  31  is so configured that a system memory  101 ,  201 , an LCD  103 ,  203 , a touch panel  105 ,  205 , a digitizer panel  107 ,  207 , a WPAN (Wireless Personal Area Network) module  109 ,  209 , a WWAN (Wireless Wide Area Network) module  111 ,  211 , a WLAN (Wireless Local Area Network) module  113 ,  213 , an SSD  115 ,  215 , and a power management unit (PMU)  117 ,  217  are connected to an SOC (System on a chip) type embedded system (Embedded System)  100 ,  200 , respectively. 
     Each of the embedded systems  100  and  200  is composed of a CPU core, a GPU, a memory controller, an I/O controller, a firmware ROM, and the like. The SSD  115 ,  215  stores software such as application programs executed by each CPU core, an operating system, and device drivers. In one example, the embedded system  100  and the embedded system  200  are connected to each other through the WPAN modules  109  and  209  when the tablet terminals  35  and  31  are connected to configure an integrated computer system. 
     Each of the WPAN modules  109  and  209  is a device for performing radio communication in any standard such as Bluetooth (registered trademark), infrared communication, or NFC communication (Near Field Communication). The embedded system  100  and the embedded system  200  may be connected through a cable interface such as USB at the time of being coupled. Items necessary to apply the disclosed embodiments in the configuration of the dual screen computer  10  in  FIG. 1A , and the configuration of the tablet terminal  51  and the smartphone  61  in  FIG. 1C  can be understood from the configuration of  FIG. 2 . 
       FIG. 3A  is a sectional view for describing the structure of the touch screen  37  mounted on the tablet terminal  35 , and  FIG. 3B  is a sectional view for describing the structure of the touch screen  33  mounted on the tablet terminal  31 . Each of the touch screens  37  and  33  has such a structure that the touch panel  105 ,  205 , the LCD  103 ,  203 , the digitizer panel  107 ,  207 , and a shield panel  81 ,  83  are laminated from the top to detect the proximity of a finger  91  in order to cause the touch panel  105 ,  205  to generate coordinate information, and to detect the proximity or a pressing force of an electronic pen  89  in order to cause the digitizer panel  107 ,  207  to generate coordinate information. 
       FIG. 4  is a functional block diagram illustrating an example of the configuration of the digitizer panel  107 , and  FIG. 5  is a functional block diagram illustrating an example of the configuration of the digitizer panel  207 . Each of the digitizer panels  107  and  207  has a transmission mode and a reception mode, and includes sensor coils  151 - 1  to  153 - m ,  251 - 1  to  253 - m  using electromagnetic wave interference with the electronic pen  89  of the type that does not require the supply of power. The electronic pen  89  includes an L-C resonant circuit formed of a coil and a capacitor. The operations of the electronic pen  89  include an up operation, a down operation, and a pen pressure operation. 
     The up operation is an operation for placing the electronic pen  89  in a position where the digitizer panel  107 ,  207  cannot detect input due to the electromagnetic wave interference, the down operation is an operation for placing the electronic pen  89  in a detectable position, and the pen pressure operation is an operation for pressing the tip of the electronic pen  89  against the surface of the touch screen  37 ,  33 . The resonant circuit of the electronic pen  89  includes a variable capacitor the capacitance of which varies depending on the magnitude of the pressure when the pen tip is pressed against the surface of the touch screen  37 ,  33  so that information corresponding to pen pressure upon drawing on paper with a pen can be detected according to a change in phase difference between excitation current in the transmission mode and induced voltage in the reception mode. 
     In coil arrays  150 ,  250 , n sensor coils  151 - 1  to  151 - n ,  251 - 1  to  251 - n  are arranged with equal pitches to overlap one another in order in the X-axis direction, and m sensor coils  153 - 1  to  153 - m ,  253 - 1  to  253 - m  are arranged with equal pitches to overlap one another in order in the Y-axis direction. Based on a selection signal received from each of controllers  165  and  265 , each of selection circuits  155 ,  255  selects the sensor coils  151 - 1  to  153 - m ,  251 - 1  to  253 - m  one by one in order to form a loop circuit that goes through each of transmitting circuits  161 ,  261  or each of receiving circuits  261 ,  263  via each of switching circuits  159 ,  259 . In response to a switching signal received from the controller  165 ,  265 , the switching circuit  159 ,  259  switches the loop circuit between the transmitting circuit  161 ,  261  and the receiving circuit  163 ,  263  alternately at predetermined time intervals multiple times while a predetermined sensor coil is being selected by the selection signal. 
     Operation during a period of selecting the transmitting circuit  161 ,  261  by the switching signal is called the transmission mode (transmission period), and operation during a period of selecting the receiving circuit  163 ,  263  is called the reception mode (reception period). The controller  165 ,  265  (a device driver therefor in practice) generates the switching signal to form multiple transmission periods and reception periods during the selection of one sensor coil. The transmitting circuit  161 ,  261  supplies high-frequency excitation current to the selected sensor coil during each transmission period. The sensor coil through which the excitation current flows emits an electromagnetic wave. The coil of the electronic pen  89  for which the down operation or the pen pressure operation is performed resonates with the electromagnetic wave and hence current flows through the resonant circuit. 
     The current flowing through the resonant circuit causes an electromagnetic wave to be emitted from the coil of the electronic pen  89 . The electromagnetic wave emitted from the coil of the electronic pen  89  is received by the same sensor coil during each reception period following the transmission period. The receiving circuit  163 ,  263  converts, to digital data, the induced voltage across the sensor coil detected during the reception period, and sends the digital data to the controller  165 ,  265 . Since the induced voltage becomes larger as the distance between the sensor coil and the electronic pen  89  is shorter, the controller  165 ,  265  can detect the induced voltage across each sensor coil selected in order while the electronic pen  89  is positioned on certain coordinates to identify a sensor coil present in a position closest to the electronic pen  89  in order to generate coordinate information. 
     The controller  165 ,  265  generates the switching signal and the selection signal, and generates the coordinate information from the induced voltage across the sensor coil. When the pen pressure operation is performed to press the electronic pen  89  against the surface of the touch screen  33 ,  37 , the capacitance of the variable capacitor of the electronic pen  89  varies to change the frequency of the current flowing through the resonant circuit. The controller  165 ,  265  calculates a difference between the frequency of the excitation current transmitted during the transmission period and the frequency of the induced voltage detected during the reception period to generate pen pressure information on the electronic pen  89 . 
     The controller  165 ,  265  sends the coordinate information and the pen pressure information to the embedded system  100 ,  200 . The pen pressure information takes a larger value as the force to depress the electronic pen  89  (pen pressure) is greater. A drawing application in the system performs processing for making a drawn line thicker as the pen pressure information exhibits a larger value. The ROM  167 ,  267  stores a reference pattern used to determine which of electronic pen input and proximity input to be described below the input pattern identified from the coordinate information and the pen pressure information is. Note that each wake-up circuit  169 ,  269  and each shutdown loop circuit  171 ,  271  that can be provided as needed to cope with a specific problem associated with the disclosed embodiments will be described later. 
     When an object displayed on the touch screen  37 ,  33  is pointed out using the electronic pen  89 , input to the software keyboard is performed, or input to a screen of the drawing application is performed, and the controller  165 ,  265  generates a corresponding coordinate signal and pen pressure information. Then, the controller  165 ,  265  processes induced voltage across all the sensor coils as input. However, the electromagnetic waves that generate the induced voltage across the sensor coils are not always emitted only from the electronic pen  89 . 
     If the housing of the tablet terminal  31  and the housing of the tablet terminal  35  are closed to make the touch screen  33  and the touch screen  37  face each other, the mutual distance between the sensor coils  151 - 1  to  153 - m  and the sensor coils  251 - 1  to  253 - m  will become short. The controller  165 ,  265  generates the selection signal and the switching signal mutually asynchronous with each other to form transmission periods and reception periods. For example, when the selected sensor coil  251 - 1  of the tablet terminal  31  is in a transmission period, if the selected sensor coil  151 - 1  of the tablet terminal  35  present in a position opposite to the tablet terminal  31  is in a reception period, induced voltage will be generated across the sensor coil  151 - 1  by an electromagnetic wave emitted from the sensor coil  251 - 1 . 
     If the receiving circuit  163  detects effective induced voltage, the controller  165  of the tablet terminal  35  will generate the coordinate information and the pen pressure information without fail. When the transmission period and the reception period of the tablet terminals  31  and  35  are reversed, the controller  265  of the tablet terminal  31  generates the coordinate information and the pen pressure information in the same way. The coordinate information and the pen pressure information generated by the controller  165 ,  265  when the touch screens  33  and  37  approach each other produce a pattern different from the coordinate information when a user performs input with the electronic pen  89 . Hereinafter, a state where the electronic pen  89  is operated to perform input is called electronic pen input, and a state where the touch screens  33  and  37  approach each other to perform pseudo input is called proximity input. 
     For example, when input to multiple coordinates at short time intervals that make it difficult for a person to perform electronic pen input is detected, the controller  165 ,  265  can determine the input to be proximity input. Further, in the case of drawing with the electronic pen  89 , the user can draw a line continuously at the maximum pen pressure recognizable by the controller  165 ,  265 , but the user rarely draws points or lines in discrete positions at the maximum pen pressure. 
     When input at the maximum pen pressure is generated on discrete coordinates, the controller  165 ,  265  can determine the input to be proximity input. Further, when input is continuously performed on two coordinates with one electronic pen  89 , the down operation and up operation for the previous coordinates are followed by the down operation for the next coordinates. When the down operations performed on multiple coordinates are detected at the same time, the controller  165 ,  264  can determine the input to be proximity input. 
     Input patterns can be classified into a pattern generated by proximity input alone, a pattern generated by electronic pen input alone, and a pattern generated by both. The input pattern generated by proximity input alone or the input pattern generated by electronic pen input alone is called a reference pattern. It is easier to create the input pattern generated by proximity input alone than the input pattern generated by electronic pen input alone. The ROM  165 ,  265  stores either or both of reference patterns. When receiving multiple pieces of digital data from the receiving circuit  163 ,  263 , the controller  165 ,  265  compares input patterns identified from temporal and spatial generation status of coordinate information and pen pressure information with the reference pattern(s) to determine whether this input is electronic pen input or proximity input. 
     When determining the input to be electronic pen input or not to be proximity input, the controller  165 ,  265  sends the coordinate information and the pen pressure information to the embedded system  100 ,  200 . When determining the input to be proximity input or not to be electronic pen input, the controller  165 ,  265  sends the embedded system  100 ,  200  a control event instead of the coordinate information and the pen pressure information. The control event can be sent using an interface between the controller  165 ,  265  and the embedded system  100 ,  200  or using a sideband. When receiving the control event, the embedded system  100 ,  200  can perform various kinds of control to be described later. 
     Note that  FIG. 1  to  FIG. 5  describes the configuration and the connection relation of the main hardware related to the embodiment simplistically to describe the embodiment. A case where multiple blocks described in the drawings are set in one integrated circuit or device, or reversely, where one block is divided to configure multiple integrated circuits or devices will be encompassed in the scope of the disclosed embodiments as long as those skilled in the art can select it arbitrarily. Further, the forms in which the components illustrated in  FIG. 1  to  FIG. 5  are changed for other components or known components are added will be encompassed in the scope of the disclosed embodiments as long as those skilled in the art can easily appreciate the forms. 
       FIG. 6  is a flowchart for describing an operation procedure when the dual screen computer  30  is closed. In block  301 , the tablet terminal  31 ,  35  becomes a power-on state, and the digitizer panel  107 ,  207  operates while repeating the transmission mode and the reception mode alternately regardless of the presence or absence of input from the electronic pen  89 . In block  303 , induced voltage is generated in the sensor coils  151 - 1  to  153 - m ,  251 - 1  to  253 - m  for some reason. The controller  165 ,  265  receives, from the receiving circuit  163 ,  263 , digital data having a size corresponding to the induced voltage generated in the sensor coils. 
     The controller  165 ,  265  generates coordinate information and pen pressure information independently of each other. In block  305 , the controller  165 ,  265  identifies an input pattern from the coordinate information and the pen pressure information, and compares the input pattern with a reference pattern stored in the ROM  167 ,  267 . When determining the input to be electronic pen input or not to be proximity input, the controller  165 ,  265  proceeds to block  351  to send the coordinate information and the pen pressure information to the embedded system  100 ,  200 . An application program in the embedded system  100 ,  200  processes the received coordinate information and pen pressure information, and the procedure returns to block  303 . 
     When determining the input to be proximity input or not to be electronic pen input, the controller  165 ,  265  does not send coordinate information and pen pressure information to the embedded system  100 ,  200 . When one of the controller  165  and the controller  265  determines the input to be proximity input ahead of the other, the one controller  165 ,  265  that has made the determination in block  307  ahead of the other generates a control event and sends the control event to a corresponding one of the embedded systems  100  and  200 . The one embedded system  100 ,  200  that has received the control event sends a message indicative of the control event to the other embedded system  100 ,  200  via the WPAN module  109 ,  209  in block  309 . In block  311 , the embedded systems  100  and  200  process the control event and make a transition to the sleep state, respectively. Specifically, the embedded systems  100  and  200  instruct the PMUs  117  and  217  to suspend power supplied to predetermined devices. 
     In blocks  305  to  311 , when either of the controllers  165  and  265  detects proximity input, the one sends a proximity event to the other and both make a transition to the sleep state, but both of the controllers  165  and  265  may detect proximity input, exchange a message indicative of the control event with each other, and make a transition to the sleep state. In this case, the probability of an erroneous determination between electronic pen input and proximity input can be reduced. 
     Since the controllers  165  and  265  operate asynchronously with each other, the time until some input is determined to be proximity input in block  305  depends on the hardware configuration and operation timing of the digitizer panel  107 ,  207 . When the search coils that face each other when approaching each other are selected at the same timing, if one operates to become a reception period when the other is in a transmission period, the occurrence of proximity input can be determined in the shortest time. 
     When the hardware configurations of the digitizer panels  107  and  207  are the same, the time required for the determination may become longer. For example, when the timings of the transmission period and the reception period of both completely match each other, a certain amount of time until one becomes the transmission period and the other becomes the reception period so that both can detect electromagnetic waves from each other is spent due to jitter of an oscillator in each of the transmitting circuits  161  and  261 . Further, if one starts selecting a search coil in the X-axis direction and the other starts selecting a search coil in the Y-axis direction when approaching each other, a certain amount of time until both can detect electromagnetic waves from each other will also be spent. 
     Although the detection time may be subjected to chance factors and hence made longer, the controllers  165  and  265  can detect proximity input without fail after a certain amount of time has elapsed. When the frequency for selecting a search coil, the frequency for switching between the transmission period and the reception period, and the number of search coils are different, proximity input can be determined in a relatively short time. When proximity input is determined in block  305 , since the embedded systems  100  and  200  do not receive coordinate information and pen pressure information, any erroneous operation of the system due to proximity input can be prevented. Note that the control event can be processed by a utility program installed on the tablet terminals  31  and  35 , respectively. 
     There is a case where either of the tablet terminals  31  and  35  makes a transition to the sleep state when the touch screens  33  and  37  approach each other, and hence power supplied to the digitizer panel  107 ,  207  is suspended. For example, when the power supplied to the digitizer panel  107  of the tablet terminal  35  is suspended, since electromagnetic wave interference does not occur between the digitizer panels  107  and  207  even if the housings are closed, proximity input cannot be detected by the method described above. 
     The shutdown loop circuits  171  and  271  deal with this problem. Each of the shutdown loop circuits  171  and  271  is configured to short-circuit all sensor coils to form a loop circuit when power supplied to the digitizer panel  107 ,  207  is suspended. A resonant element may be inserted in each of the shutdown loop circuits  171  and  271  as needed. In this case, for example, even when the tablet terminal  35  is shifted to the sleep state, electromagnetic waves emitted from the sensor coils  251 - 1  to  253 - m  of the digitizer panel  207  during each transmission period causes excitation current to flow through the sensor coils  151 - 1  to  153 - m  of the digitizer panel  107  to emit an electromagnetic wave so that the digitizer panel  207  can detect the electromagnetic wave during each reception period to detect proximity input. 
     In the sleep state, there is a method of suspending the power supply to many peripheral devices, including the digitizer panels  107  and  207 , when the CPU utilization drops down to cause the CPU cores to make a transition between an active state (C 0  state) and a sleep state (C 1  state to Cn state) at fixed intervals. As an example, such a method is realized by a function called Connected Standby on Windows (registered trademark) 8. 
     In the case of Connected Standby, the shutdown loop circuits  171  and  271  mentioned above are provided in the digitizer panels  107  and  207 . Suppose that the housings are closed when both are in the Connected Standby mode. In this case, if the digitizer panels  107  and  207  are configured to be supplied with power when the CPU core in one of the tablet terminals  35  and  33  makes a transition to the active state, the one tablet terminal, e.g., the tablet terminal  35 , which made the transition to the active state, can detect proximity input, and the other tablet terminal, i.e., the tablet terminal  31  that makes a transition to the active state after that can detect proximity input. 
     Next, a method of synchronizing and transferring data in a dual digitizer system configured to include the tablet terminal  51  and the smartphone  61  shown in  FIG. 1C  will be described. The description will be made by associating the configuration of the tablet terminal  51  with that of the tablet terminal  35  in  FIG. 2 , and associating the configuration of the smartphone  61  with that of the tablet terminal  31  in  FIG. 2 . It is assumed here that the tablet terminal  51  is shifted to the sleep state in which power supplied to most devices, including the digitizer panel  107 , except a device for maintaining the storage of the system memory  101  is suspended like the suspend state. At this time, the smartphone  61  in which the digitizer panel  207  is operating is so overlapped that the touch screen  63  will face the touch screen  53 . 
     If the digitizer panel  107  of the tablet terminal  51  is equipped with the shutdown loop circuit  171 , the smartphone  61  can detect a proximity event. However, the tablet terminal  51  cannot detect proximity input unless a wake event is given from the outside to come into the power-on state. The wake-up circuit  169  (the same applies to the wake-up circuit  269 ) wakes up the tablet terminal  51  in the suspend state by the proximity of the smartphone  61  to deal with this problem. 
     The wake-up circuit  169  is supplied with power even in the suspend state to detect voltage induced by an electromagnetic wave emitted from the digitizer panel  207  of the smartphone  61  to each of the sensor coils  151 - 1  to  153 - m  that form the shutdown loop circuit  171 . The wake-up circuit  169  generates a wake event when detecting predetermined voltage across multiple sensor coils, and sends the wake event to the PMU  117 . The PMU  117  that has received the wake event supplies power to the embedded system  100  and peripheral devices to shift the system to the power-on state. 
       FIG. 7  is a diagram for describing a state of synchronizing or transferring data between the tablet terminal  51  and the smartphone  61 , and  FIG. 8  is a flowchart showing the operation procedure. Such a scenario that data created or received by using the smartphone  61  on the go is transferred to the tablet terminal  51  in the office or synchronized with data updated on the tablet terminal  51  is assumed. 
     Coordinate domains  501  and  503  are defined for the digitizer panel  107  on the coordinates of the touch screen  53  of the tablet terminal  51 . The coordinate domains  501  and  503  have almost the same size as the Smartphone  61  to overlap the Smartphone  61 . In the SSDs  115  and  215 , a docking application for processing data transfer is stored. The docking application on the tablet terminal  51  assigns data synchronization to the coordinate domain  501 , and assigns data transfer to the coordinate domain  503 . When the area of the touch screen  53  is large, the number of coordinate domains can be three or more. 
     The data synchronization means processing for replacing data on application programs pre-registered in the docking application with the latest data between the smartphone  61  and the tablet terminal  51 . The data transfer means processing for transferring data on application programs pre-registered in the docking application from either one of the smartphone  61  and the tablet terminal  51  to the other. In block  501  of  FIG. 8 , the smartphone  61  in the power-on state is overlapped with the coordinate domain  501  or the coordinate domain  503  on the touch screen  53  in such a manner that the touch screen  63  faces the touch screen  53 . The user selects a coordinate domain with which the smartphone  61  is overlapped to reflect a user&#39;s intention for either transfer or synchronization. 
     The smartphone  61  generates a control event in the procedure described with reference to  FIG. 6  to run the docking application. The following shows the operation of the tablet terminal  51  from block  503  to block  515 . In block  503 , when the tablet terminal  51  is shifted to the suspend state, the procedure moves to block  505 , while when it is shifted to the power-on state or the Connected Standby state, the procedure moves to block  511 . In block  505 , the wake-up circuit  169  detects the proximity of the smartphone  61  to generate a wake event, and in block  509 , the tablet terminal  51  makes a transition to the power-on state. 
     In block  511 , the controller  165  detects proximity input. In block  513 , the controller  165  generates coordinate information. In block  515 , the controller  165  determines in which of the coordinate domain  501  and the coordinate domain  503  the input coordinates corresponding to the input determined to be proximity input have been generated. When detecting proximity input to the coordinate domain  501 , the controller  165  generates a synchronization event and sends it to the embedded system  100 . The docking application on the embedded system  100  that has received the synchronization event prepares for synchronization, and sends a message indicative of the synchronization event to the smartphone  61  through the WPAN module  109  in block  517 . 
     The docking application on the embedded system  200  that has received the message prepares for synchronization. After that, the synchronization of predetermined data is performed between the docking application on the embedded system  100  and the docking application on the embedded system  200 . Upon completion of the synchronization, the procedure moves to block  519  in which the tablet terminal  51  makes a transition to the suspend state. 
     In block  515 , when detecting proximity input to the coordinate domain  503 , the controller  165  generates a transfer event and sends it to the embedded system  100 . The docking application on the embedded system  100  prepares for data transfer, and sends a message indicative of the transfer event to the smartphone  61  through the WPAN module  109 . The transfer of predetermined data from the smartphone  61  to the tablet terminal  51  is assumed here, but the direction of the transfer may be reversed. 
     The docking application on the embedded system  200  that has received the message prepares for data transfer. After that, the predetermined data is transferred from the Smartphone  61  to the tablet terminal  51  through the WPN module  209 . As an example, the data to be transferred can be the URL of a web browser displayed on the smartphone  61 . The tablet terminal  51  that has received the URL can display the same screen as that of the smartphone  61  in block  523 . In this case, the same screen as that displayed on the smartphone  61  can be displayed on the large touch screen  53  of the tablet terminal  51  with simple operations. 
     Although the procedure for generating a control event when digitizers approach each other has been described with reference to  FIG. 6  and  FIG. 8 , the control event can also be generated when the touch screen is covered with a cover.  FIG. 9  shows a state where loop coils  501  and  503  are attached to a cover  500  of the tablet terminal  51 . When the surface of the touch screen  53  is covered with the cover  500  and electromagnetic wave interference between the loop coils  501  and  503  is detected, the digitizer panel  107  can determine proximity input and generate a close event. At this time, a predetermined control event can also be assigned to a pattern formed by providing two or more coordinate domains. 
     While the disclosed embodiments has been described so far with reference to the specific embodiment shown in the drawings, the disclosed embodiments are not limited to the embodiment shown in the drawings. It is needless to say that any known configuration can be employed as long as the configuration has the effects of the disclosed embodiments.