Abstract:
Provided are an electronic control device and a microcomputer control method not only enabling smooth transmission and reception of signals by using a plurality of microcomputers but also capable of achieving, with a simpler configuration, reduction of power consumed by the microcomputers. As a mode for reducing power consumption, the electronic control device brings microcomputers from which a sleep request has been issued into a sleep state. The electronic control device is equipped with a low power consumption mode for bringing a communication bus driver into the sleep state after all microcomputers constituting the electronic control device have been transferred into the sleep state.

Description:
FIELD OF THE DISCLOSURE 
     The present invention relates to an electronic control device having microcomputers, and a method of controlling the microcomputers. 
     BACKGROUND OF THE DISCLOSURE 
     Typically in vehicles such as automobiles, many electronic control devices are installed. A leading example of such electronic control devices is an electronic control device that forms a part of a navigation system, and other examples are electronic control devices for use in controlling a variety of in-vehicle devices (e.g., the engine and the brakes) with microcomputers or for use in controlling condition display devices adapted to display a variety of vehicle conditions (e.g., the meters). In such vehicles, these electronic control devices are electronically connected with one another by communication lines to form a vehicle network. Through such vehicle network, a variety of vehicle data is transmitted and received between the electronic control devices. 
     As disclosed in Patent Document 1, microcomputers have been proposed that is switched to a power saving mode (i.e., a mode during which power consumption is reduced by stopping the oscillation of the clock signal while maintaining the internal conditions) when there is no need for microcomputers to conduct any processing (e.g., when the vehicle is stopped). In such electronic control device having microcomputers switchable to a power saving mode, the microcomputers are switched between the power saving mode and the normal power mode in accordance with the vehicle conditions, such that the power consumed in the electronic control device is reducible. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2008-123538 
     SUMMARY OF THE INVENTION 
     Problems that the Invention is to Solve 
     In recent years, the number of the electronic control devices installed in a vehicle has been increased in accordance with the advance of the vehicle performance. Since the increase in the number of the electronic control devices connected to the vehicle network increases the length of the wiring paths of the communication lines, designing of the paths while securing the communication quality may become complicated or the communication quality may be reduced. 
     With the above background, it has been proposed that microcomputers (control circuits)  50   a  and  50   b , each of which is usually provided per electronic control device, be provided altogether to a single electronic control device  10  as depicted in, for instance,  FIG. 12 . In the electronic control device  10  having the microcomputers  50   a  and  50   b , the microcomputers  50   a  and  50   b  share a single transceiver  30  for transmitting and receiving vehicle data. 
     However, in a configuration where the transceiver  30  is shared as described above, an arbiter  20  adapted to arbitrate the control signals output from the microcomputers  50   a  and  50   b  needs to be provided between the transceiver  30  and the microcomputers  50   a  and  50   b . Further, in order to provide the power saving function to the electronic control device  10  having the microcomputers  50   a  and  50   b , the electronic control device  10  needs to perform a process for switching the microcomputers  50   a  and  50   b  to the power saving mode, which requires the arbiter  20  to have more advanced functions. In other words, the configuration where the transceiver  30  is shared by the microcomputers complicates the configuration of the electronic control device. 
     The problems described above are not unique to electronic control devices for use in vehicles, but almost common to any electronic control devices having microcomputers. 
     Accordingly, it is an objective of the present invention to provide an electronic control device and a method of controlling microcomputers, according to which signals from a plurality of microcomputers are smoothly transferred; and the power consumed by the microcomputers is reduced with a simple configuration. 
     Means for Solving the Problems 
     To achieve the foregoing objective and in accordance with the present invention, an electronic control device is provided that includes a plurality of microcomputers. The electronic control device communicates with other devices through communication lines. The microcomputers share a communicator, which is provided between the microcomputers and the communication lines and adapted to transmit and receive signals. A power saving mode is performed to reduce power consumed by the electronic control device. The power saving mode is a mode during which any of the microcomputers that have made a sleep request are switched to a sleeping mode, and the communicator is switched to the sleeping mode after all the microcomputers have shifted to the sleeping mode. 
     To achieve the foregoing objective and in accordance with the present invention, a method of controlling a plurality of microcomputers included in an electronic control device adapted to conduct communication with other devices is provided. The method includes: causing the microcomputers to share a communicator provided between communication lines and adapted to transmit and receive a signal; and switching the electronic control device to a power saving mode during which power consumed by the electronic control device is reduced. The step of switching the electronic control device to the power saving mode includes: a first step during which microcomputers for which sleep requests are made are switched to sleeping mode; and a second during which the communicator is switched to the sleeping mode after all the microcomputers have shifted to the sleeping mode. 
     Typically in an electronic control device including a single microcomputer and a single communicator, when the microcomputer shifts to the sleeping mode, the communicator also shifts to the sleeping mode in accordance therewith. Therefore, when the electronic control device includes a plurality of thus-controlled microcomputers and one of such microcomputers shifts to the sleeping mode, the communicator also shifts to the sleeping mode in accordance therewith, a result of which is that the other microcomputers sharing the same communicator are not able to continue the communication. 
     According to the above configuration or method, the communicator does not shift to the sleeping mode when only one of the microcomputers included in the electronic control device has shifted to the sleeping mode. Therefore, the other microcomputers remaining in the normal operation mode without shifting to the sleeping mode are able to continue the communication via the communicator with the other electronic control devices connected to the same communicator. When all the microcomputers included in the electronic control device have shifted to the sleeping mode, the communicator also shifts to the sleeping mode in accordance therewith. Accordingly, until all the microcomputers included in the electronic control device have shifted to the sleeping mode, the signal transmission and reception via the communicator is continued. Further according to the above configuration or method, in order to switch the microcomputers and the communicator to the sleeping mode, there is no need to provide a control circuit between the communicator and the microcomputers for controlling the operation conditions of the microcomputers and the signals transmitted from the microcomputers. Therefore, the electronic control device having the microcomputers is simply configured. With this arrangement, the power consumed by the microcomputers is reduced with a more simplified configuration while securing the smooth transfer of the signal by the microcomputers. 
     In accordance with one aspect of the present invention, each of the microcomputers includes a standby terminal whose condition is selectively set to “H” logic level, “L” logic level or high impedance in relation to the communicator. The communicator shifts to the sleeping mode when any one of the standby terminals of the microcomputers is set to the “L” logic level. The microcomputers shifting to the sleeping mode switch outputs of the standby terminals to the high impedance at the time of shifting to the power saving mode. 
     Typically, when the standby terminal included in the microcomputer is switched to the “L” logic level, the communicator shifts to the sleeping mode in accordance therewith. In addition, since the “L” logic level is superior to the “H” logic level, the “L” logic level will be prioritized if some standby terminals of the microcomputers are set to “L” while others are set to “H” in a mixed manner. If so prioritized, the communicator may shift to the sleeping mode. More specifically, even when some microcomputers exhibit the “H” logic level and are continuously in communication, the communicator, which relays the signal of the microcomputers, may shift to the sleeping mode. 
     According to the above configuration, the standby terminals (STBN) of the microcomputers to be switched to the sleeping mode are set to high impedance, and thus the communicator does not shift to the sleeping mode in accordance with the high impedance. In other words, without affecting the operation conditions of the communicator, some of the microcomputers are switched to the sleeping mode. 
     In accordance with one aspect of the present invention, at the time of shifting to the power saving mode, after the standby terminals of the microcomputers are sequentially switched to the high impedance, the standby terminal of the microcomputer that lastly shifts to the sleeping mode is switched to the “L” logic level. 
     In accordance with one aspect of the present invention, each of the microcomputers is provided with a standby terminal whose condition is selectively set to “H” logic level, “L” logic level or high impedance in relation to the communicator. The communicator shifts to the sleeping mode when any one of the standby terminals of the microcomputers is set to the “L” logic level. The first step includes: sequentially switching the standby terminals of the microcomputers to the high impedance; and switching the standby terminal of the microcomputer that lastly shifts to the sleeping mode to the “L” logic level. 
     According to the above configuration or method, the standby terminals of the microcomputers shifting to the sleeping mode are sequentially switched to the high impedance, and only the standby terminal of the microcomputer that lastly shifts to the sleeping mode is switched to the “L” logic level. Thus, when the standby terminal of the microcomputer that lastly shifts to the sleeping mode has been switched to the “L” logic level, the communicator shifts to the sleeping mode. Accordingly, until the standby terminal of the microcomputer that lastly shifts to the sleeping mode is switched to the “L” logic mode, the operation conditions of the communicator are reliably maintained, and the communication via the communicator is also reliably maintained. Therefore, with use of the logic level settable to the standby terminals of the microcomputers and the conditions of the standby terminals, the operation conditions of the communicator are reliably controlled. 
     In accordance with one aspect of the present invention, at the time of shifting to the power saving mode, if the microcomputers shift to the sleeping mode simultaneously, the standby terminals of the microcomputers are switched to the “L” logic level simultaneously as a special exception. 
     In accordance with one aspect of the present invention, each of the microcomputers is provided with a standby terminal whose condition is selectively set to “H” logic level, “L” logic level or high impedance in relation to the communicator. The communicator shifts to the sleeping mode when any one of the standby terminals of the microcomputers is set to the “L” logic level. The first step includes switching the standby terminals of the microcomputers to the “L” logic level simultaneously as a special step for switching the microcomputers to the sleeping mode simultaneously. 
     According to the above configuration or method, if the microcomputers included in the electronic control device are switched to the sleeping mode simultaneously, the standby terminals of the microcomputers are collectively switched to the “L” logic level. Therefore, even if the microcomputers shift to the sleeping mode simultaneously, the communicator shifts to the sleeping mode in accordance with the sleeping mode of the microcomputers. 
     In accordance with one aspect of the present invention, the microcomputers are connected with one another by a dedicated communication line and adapted to transmit through the dedicated communication line information indicative of shifting to the sleeping mode. Each of the microcomputers monitors operation conditions of the other microcomputers sharing the communicator based on the information transmitted through the dedicated communication line. Based on the monitored operation conditions, each of the microcomputers determines whether the same microcomputer is required to set the standby terminal of the same microcomputer to the high impedance or to the “L” logic level at the time of shifting to the sleeping mode. 
     In accordance with one aspect of the present invention, the microcomputers are connected with one another by a dedicated communication line and adapted to transmit through the dedicated communication line information indicative of shifting to the sleeping mode. Each of the microcomputers monitors operation conditions of the other microcomputers based on the information transmitted through the dedicated communication line. Based on the monitored operation conditions, each of the microcomputers determines whether the same microcomputer is required to set the standby terminal of the same microcomputer to the high impedance or to the “L” logic level at the time of shifting to the sleeping mode. 
     According to the above configuration or method, the microcomputers are each capable of monitoring the other microcomputers sharing the same communicator, based on the signal transmitted through the dedicated communication lines connecting the microcomputers. Therefore, the microcomputers are each capable of constantly monitoring whether or not the other microcomputers sharing the same communicator have shifted to the sleeping mode, and thus capable of determining whether its own standby terminal should be set to the high impedance or the “L” logic level when the same microcomputer shifts to the sleeping mode, based on the monitoring results. Accordingly, the conditions of the standby terminals of the microcomputer are accurately determined, and the operation conditions of the communicator that shifts to the sleeping mode in accordance with the conditions of the standby terminals are controlled at higher accuracy. 
     In accordance with one aspect of the present invention, when a signal is input from control targets that the microcomputers control, the sleeping mode of the relevant microcomputers is cancelled. When the communicator receives a signal transmitted from an electronic control device different from the electronic control devices remaining in the sleeping mode, the power saving mode of the electronic control devices remaining in the sleeping mode is cancelled. 
     In accordance with one aspect of the present invention, the method of controlling microcomputers further includes: cancelling the sleeping mode of the microcomputers when a signal is input from control targets that the microcomputers control; and cancelling the power saving mode of the electronic control devices remaining in the sleeping mode when the communicator receives a signal transmitted from an electronic control device different from the electronic control devices remaining in the sleeping mode. 
     According to the above configuration or method, when a signal is output from the control targets that the microcomputers control, the sleeping mode of the microcomputers is cancelled, and the microcomputers perform the various controls in accordance with the signals input from the control targets. Further according to the above configuration or method, when the communicator receives a signal from any one of the other electronic control devices connected to the communication line, the power saving mode of the electronic control device is cancelled. Then, the microcomputers included in the electronic control device perform the controls in accordance with the signal received by the communicator. Therefore, the sleeping mode of the microcomputers is maintained until the various controls by the microcomputers included in the electronic control device become necessary. On the other hand, when such various controls become necessary, the sleeping mode of the microcomputers is cancelled, and thereafter the microcomputers perform the controls as required. Accordingly, while securing the time period during which the electronic control device performs the power saving mode and reducing the power consumption, the functions required for the electronic control devices are maintained. 
     In accordance with one aspect of the present invention, at the time of cancelling the power saving mode, based on input of a signal from a control target that any one of the microcomputers controls, the sleeping mode of the microcomputers that have input the signal is cancelled, and thereafter the sleeping mode of the communicator and the sleeping mode of the microcomputers that have not input the signal from the control target are cancelled. 
     In accordance with one aspect of the present invention, the step of cancelling the sleeping mode of the microcomputers sequentially: cancels the sleeping mode of a microcomputer that has input a signal from a control target that any one of the microcomputers controls, based on the input of the signal; and cancels the sleeping mode of the microcomputers that have not input the signal from the control target. 
     According to the above configuration or method, when a signal is transmitted from the control targets of a microcomputer due to occurrence of an event and the transmitted signal is input in the microcomputer, the sleeping mode of the microcomputer is cancelled. Subsequently, the sleeping mode of the communicator and the sleeping mode of the other microcomputers that have not input the signal from the control target are cancelled. Therefore, once the signal is input in the microcomputer from the control target, the sleeping mode of the same microcomputer, the communicator and the other microcomputers is suitably cancelled, and various controls based on the signal input from the control target are performed. Accordingly, the sleeping mode of the microcomputers is cancelled at a right timing, and various controls are smoothly performed by the microcomputers switched off from the sleeping mode. 
     In accordance with one aspect of the present invention, at the time of cancelling the power saving mode, after the sleeping mode of the communicator is cancelled based on input of a signal from the different electronic control device, the sleeping mode of all the microcomputers is cancelled. 
     In accordance with one aspect of the present invention, the step of cancelling the power saving mode sequentially: cancels the sleeping mode of the communicator based on input of a signal from the different electronic control device; and cancels the sleeping mode of all the microcomputers. 
     According to the above configuration or method, when a signal transmitted from a different electronic control device is input in the communicator of the electronic control device due to occurrence of an event, the sleeping mode of the communicator that has input the signal is cancelled. Subsequently, the sleeping mode of the microcomputers sharing the communicator is cancelled. Therefore, when the signal is input in the electronic control device from a different electronic control device, the sleeping modes of the communicator and microcomputers included in the electronic control device are suitably cancelled, and various controls based on the signal input from the control target are performed by the same electronic control device. Accordingly, the sleeping mode of the microcomputers is cancelled at a right timing, and the microcomputers having switched off from the sleeping mode more smoothly perform various controls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram depicting an electronic control device and a method of controlling microcomputers according to one embodiment of the present invention, more specifically depicting an example of a vehicle network formed by an electronic control device having microcomputers; 
         FIG. 2  is a block diagram schematically depicting a configuration of the electronic control device having the microcomputers; 
         FIG. 3  is a flowchart depicting a switching procedure for switching to a power saving mode according to the embodiment; 
         FIG. 4  is a flowchart depicting an example of a periodical transmission procedure of data frame transmitted by the microcomputers; 
         FIG. 5  is a flowchart depicting a turn-off procedure of the power saving mode according to the embodiment; 
         FIG. 6  is a sequence diagram depicting a switching operation of an operation mode when the microcomputers included in the electronic control device make sleep requests at different timings; 
         FIG. 7  is a sequence diagram depicting a switching operation of an operation mode when the microcomputers included in the electronic control device make sleep requests at the same timing; 
         FIG. 8  is a sequence diagram depicting a return operation returning from the power saving mode to a normal operation mode when a control signal is input in a first microcomputer; 
         FIG. 9  is a sequence diagram depicting a return operation returning from the power saving mode to the normal operation mode when a communication bus driver of a first electronic control device receives a signal transmitted by a second electronic control device; 
         FIG. 10  is a timing diagram depicting: a shifting operation for shifting to the power saving mode when the microcomputers of the electronic control device make the sleep requests at different timings; and a turn-off operation of the power saving mode when a control signal is input in the first microcomputer; 
         FIG. 11  is a timing diagram depicting: a shifting operation for shifting to the power saving mode when the microcomputers included in the electronic control device make the sleep requests at the same timing; and a turn-off operation of the power saving mode when the communication bus driver of the first electronic control device receives a signal transmitted by the second electronic control device; and 
         FIG. 12  is a block diagram schematically depicting a configuration of a known electronic control device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the description below, an electronic control device and a method of controlling microcomputers according to one embodiment of the invention will be described with reference to  FIGS. 1 to 11 . The electronic control device and the method of controlling the microcomputers according to the present embodiment are applicable to an electronic control device connected to a vehicle network installed in a vehicle. 
     As depicted in  FIG. 1 , a vehicle C includes a control network including: electronic control devices (ECU)  100 A to  100 F adapted to electronically control a variety of vehicle devices such as engine and brake; and a communication line BS 1 . The control network is standard equipment serving as the core system. The vehicle C further includes a body network including: electronic control devices  100 G to  100 I adapted to control body devices such as meters for displaying a variety of vehicle conditions and air conditioners; and a communication line BS 2 , and the body network also serves as the core system. The vehicle C still further includes an information network including: electronic control devices  100 J to  100 M adapted to control a variety of information devices (e.g., a car navigation system for navigating the vehicle from the current point to the destination); and a communication line BS 3 . 
     The electronic control devices  100 A to  100 F included in the control network are, for instance, operative both while the ignition of the vehicle is turned off and while the ignition of the vehicle is turned on. The electronic control devices  100 G to  100 I included in the body network are, for instance, not operative while the ignition of the vehicle is turned off, but operative while the ignition of the vehicle is turned on. Further, the electronic control devices  100 J to  100 M included in the information network are, for instance, not operative while the accessories of the vehicle are turned off, but operative while the accessories of the vehicle are turned on. 
     The above networks are electrically connected with one another via, for instance, a gateway  100 N also usable for relaying data communication with wireless communication devices. With this arrangement, for instance, the car navigation system performs various display supports for the driver based on the information about the vehicle operations obtained from various electronic control devices such as an engine controller and brake controller. 
     Further, for instance, the communication line BS 1  (BS 2 , BS 3 ) to which the electronic control device  100 A (whose configuration is schematically depicted in  FIG. 2 ) is connected is a multiplex communication line for use in multiplex communication by time division. The communication line BS 1  includes a pair of communication lines BS 1   a  and BS 1   b  made of CANH and CANL, both ends of which are mutually connected by a terminator. The communication line BS 1  serves as a CAN (control area network) that transmits data with use of the two lines of BS 1   a  and BS 1   b , and performs a bus communication based on the differential voltage between the communication lines BS 1   a  and BS 2   b  in accordance with a predetermined communication protocol. 
     The electronic control device  100 A exemplarily includes a first microcomputer  110  and a second microcomputer  120  adapted to perform computing processing. The first microcomputer  110  and the second microcomputer  120  respectively perform different controls in accordance with the functions assigned thereto. Further, the electronic control device  100 A includes: a communication bus driver  130  (serving as a communicator) connected to the communication lines BS 1   a  and BS 1   b  and adapted to transmit and receive data via the communication lines BS 1   a  and BS 1   b ; and internal memories ROM, RAM and the like (not depicted) for storing a variety of programs and data. In the present embodiment, since the single electronic control device  100 A includes the two microcomputers  110  and  120 , the microcomputers  110  and  120  share the communication bus driver  130 . 
     The microcomputers  110  and  120  control the communication bus driver  130  such that the differential voltage is generated between the communication lines BS 1   a  and BS 1   b  at the time of data transmission in accordance with the transmitted data, and also receive data demodulated by the communication bus driver  130 . 
     The microcomputers  110  and  120  respectively include communication controllers  111  and  121  adapted to control the transmission and reception of signals by the microcomputers  110  and  120 . The communication controllers  111  and  121  provided respectively to the microcomputers  110  and  120  are connected with each other via a communication line  140 . In addition, the communication controllers  111  and  121  are connected to a communication controller  131  provided to the communication bus driver  130  via a communication line  141 . With such arrangements, signals are transferred between the microcomputers  110  and  120  and the communication bus driver  130  via the communication lines  140  and  141 . 
     The microcomputers  110  and  120  respectively include standby terminals (STBN)  112  and  122  adapted to selectively output “high (H)” and “low (L)” logic level signals. The standby terminals  112  and  122  according to the present embodiment include, for instance, a three-state buffer, so that not only the outputting of the “H” and “L” signals is enabled, but also the switching to high impedance is enabled. The standby terminals  112  and  122  are connected via the communication line  142  to an input standby terminal  132  provided to the communication bus driver  130 . 
     The microcomputers  110  and  120  respectively further include wake-up terminals  113  and  123  into which signals for returning the microcomputers having shifted to the sleep mode to a wake-up mode (e.g., an “L” logic level signal) are input from a wake-up terminal  133  provided to the communication bus driver  130 . The wake-up terminals  113  and  123  are connected via the communication line  143  to the wake-up terminal  133  provided to the communication bus driver  130 . 
     The communication bus driver  130  is controlled based on the transmission command input from the microcomputers  110  and  120  such that a predetermined differential voltage is generated between the CANH and CANL of the communication lines BS 1   a  and BS 1   b . The communication bus driver  130  further detects as a signal the differential voltage generated between the CANH and CANL of the communication lines BS 1   a  and BS 1   b , and demodulates the received data. Then, the communication bus driver  130  transmits the data to the microcomputers  110  and  120 . 
     The voltage applied to the CANH of the commutation line BS 1  from the communication bus driver  130  is typically adjusted to conform to either the dominant side (e.g., 3.5 V) or the recessive side (e.g., 2.5 V). In addition, the voltage applied to the CANL of the communication line BS 1  from the communication bus driver  130  is typically adjusted to conform to either the dominant side (e.g., 1.5 V) or the recessive side (e.g., 2.5 V). 
     The electronic control device  100 A configured as described above shifts from the normal operation mode to the power saving mode (i.e., a mode during which the processing for reducing the power consumption is performed) when the occurrence of events (e.g., turning on of the ignition while the ignition of the vehicle C is cancelled, opening of the door, reception of radio signals, or reception of bus edges from the other electronic control devices  100 B to  100 M) has not been detected for a long time. The power saving mode according to the present embodiment refers to a mode during which all the microcomputers  110  and  120  included in the electronic control device  100 A and the communication bus driver  130  have shifted to a sleeping mode. 
     When the occurrence of an event is detected during the power saving mode while the ignition is cancelled, the electronic control device  100 A cancels the power saving mode to be activated. Then, after the activation, the electronic control device  100 A shifts to the wake-up mode during which the communication via the communication lines BS 1   a  and BS 1   b  is enabled. Further, when inputting a signal in accordance with the occurrence of an event such as the reception of bus edges from the other electronic control devices  100 B to  100 M, the electronic control device  100 A shifts to the wake-up mode from the power saving mode. 
     The next description will describe procedures for switching the operation mode of the microcomputers in the electronic control device and the method of controlling the microcomputers according to the present embodiment, with reference to the flowcharts depicted in  FIGS. 3 to 5 . 
     As depicted in  FIG. 3  as step S 100 , when the control over the control target by the first microcomputer  110  (microcomputer M1) becomes unnecessary due to, for instance, a stop of the vehicle C, a declaration is made that the first microcomputer  110  will shift to the sleeping mode, in order to reduce the power consumed by the first microcomputer  110 . At this time, the standby terminals  112  and  122  of the microcomputers  110  and  120 , which are in the wake-up mode, are exemplarily set to be the “H” logic level. The first microcomputer  110  and the second microcomputer  120  (microcomputer M2) control, for instance, an engine injection nozzle and steering (i.e., control targets not depicted) without using the communication bus driver  130 . 
     The first microcomputer  110  according to the present embodiment transmits through the communication lines  140  and  141  data frame that indicates that the first microcomputer  110  shifts to the sleeping mode. The data frame thus transmitted though the communication lines  140  and  141  are sent to the second microcomputer  120 , and further sent to the other electronic control devices  100 B to  100 M via the communication bus driver  130  (step S 101 ). 
     In the present embodiment, as depicted in  FIG. 4  as step S 200 , data frame that indicates whether the microcomputers  110  and  120  are in the sleeping mode or the wake-up mode is periodically transmitted through the communication lines  140  and  141  as well as through the communication lines BS 1  to BS 3 . With such arrangements, in the present embodiment, the second microcomputer  120  and the other electronic control devices  100 B to  100 M are capable of monitoring the conditions of the first microcomputer  110 . Likewise, as data frame that indicates the conditions of each microcomputer is transmitted from the second microcomputer  120  and other microcomputers included in the electronic control devices  100 B to  100 M each, the first microcomputer  110  is also capable of monitoring the conditions of the other microcomputers. 
     As depicted in  FIG. 3  as step S 102 , a determination is made on whether or not the microcomputers  110  and  120  included in the electronic control device  100 A have made the sleep requests simultaneously. Subsequently, when the sleep requests are made at different timings, then a determination is made on whether or not all microcomputers included in the same electronic control device have already shifted to the sleeping mode or whether or not all such microcomputers are making the sleep requests (step S 103 ). More specifically, a determination is made on whether or not the second microcomputer  120 , which shares the communication bus driver  130  with the first microcomputer  110  having made the sleep request during the step S 100 , has already shifted to the sleeping mode, or on whether the second microcomputer  120  is making the sleep request. 
     When the second microcomputer  120  has neither shifted to the sleeping mode nor is making the sleep request (step S 103 : NO), the first microcomputer  110  changes the logic level of the standby terminal  112  of the microcomputer  110  from “H” to high impedance (step S 104 ). When the standby terminal  112  of the microcomputer  110  is changed to high impedance as described above, the first microcomputer  110  shifts from the wake-up mode to the sleeping mode (step S 105 ). 
     On the other hand, when the second microcomputer  120  has already shifted to the sleeping mode or is making the sleep request (step S 103 : YES), the first microcomputer  110  changes the logic level of the standby terminal  112  of the first microcomputer  110  from “H” to “L” (step S 106 ). More specifically, the first microcomputer  110  determines itself as the microcomputer that lastly shifts to the sleep mode in the electronic control device  100 A, and changes the logic level of itself to “L”, thereby shifting to the sleeping mode from the wake-up mode. With the logic level of the standby terminal  112  of the first microcomputer  110  changed to “L”, the communication bus driver  130 , which has input the logic level “L”, shifts to the sleep mode from the wake-up mode (step S 107 ). In this manner, the electronic control device  100 A shifts to the power saving mode from the normal operation mode. The standby terminal  112  whose logic level has been changed to “L” will be changed to high impedance after lapse of a predetermined time. 
     On the other hand, if the microcomputers  110  and  120  included in the electronic control device  100 A make the sleep requests simultaneously (step S 102 : YES), the logic levels of the standby terminals  112  and  122  are changed from “H” to “L” (step S 108 : YES, S 109 ). By this operation, all the microcomputers  110  and  120  included in the electronic control device  100 A shift to the sleeping mode, and the communication bus driver  130  shifts from the wake-up mode to the sleeping mode. In this way, the electronic control device  100 A shifts from the normal operation mode to the power saving mode. At this time as well, the standby terminal  112  whose logic level has been set to “L” is changed to high impedance after lapse of a predetermined time. 
     Next, as depicted in  FIG. 5 , when the power saving mode is to be cancelled, first of all, a determination will be made during a step S 300  on whether or not a signal is input in either the microcomputer  110  or  120  from the control targets of the microcomputers  110  and  120 . If a signal is input into the microcomputer  110  from, for instance, the control target that the microcomputer  110  controls, the standby terminal  112  of the microcomputer  110  is changed from high impedance to “H” logic level (step S 301 ). 
     Subsequently, the signal of the “H” logic level is input into the standby terminal  132  of the communication bus driver  130  via the communication line  142  (step S 302 ). In accordance therewith, the communication bus driver  130  shifts to the wake-up mode from the sleeping mode. Then, the communication bus driver  130  having shifted to the wake-up mode outputs the signal of “L” logic level from the wake-up terminal  133  of the communication bus driver  130  (step S 303 ). 
     Subsequently, the signal of the “L” logic level output from the wake-up terminal  133  is input into the wake-up terminals  113  and  123  of the microcomputers  110  and  120 . With this operation, the second microcomputer  120 , which has shifted to the sleeping mode, shifts to the wake-up mode. Then, the second microcomputer  120  switches the standby terminal  122  of the second microcomputer  120  from the high impedance to the “H” logic level (step S 304 ). By this way, the microcomputers  110  and  120  included in the electronic control device  100 A and the communication bus driver  130  shift from the sleeping mode to the wake-up mode, thereby cancelling the power saving mode of the electronic control device  100 A. 
     On the other hand, when no control signal is input from the control targets into the microcomputer  110  or  120  during the step S 300  (step S 300 : NO), a determination is made on whether or not the communication bus driver  130  has received a signal from any one of the electronic control devices  100 B to  100 M (i.e., electronic control device other than the electronic control device having the communication bus driver  130 ) (step S 305 ). In other words, whether or not the voltage of the communication line BS 1  connected to the communication bus driver  130  has been changed is determined. Then, when the signal transmitted from any one of the electronic control devices  100 B to  100 M is input into the communication bus driver  130  of the electronic control device  100 A (step S 305 : YES), the logic level of the standby terminal  132  of the communication bus driver  130  is changed to “H” (step S 302 ). Subsequently, the wake-up terminal  133  of the communication bus driver  130  outputs the signal of the “L” logic level, and this signal is input into the wake-up terminals  113  and  123  of the microcomputers  110  and  120  (step S 303 ). Then, the microcomputers  110  and  120 , whose wake-up terminals  113  and  123  have input the signal of the “L” logic level, shift to the wake-up mode from the sleeping mode (step S 304 ). In this way, the power saving mode of the electronic control device  100 A is cancelled. 
     In the next description, the operation of the microcomputers in the electronic control device and the method of controlling the microcomputers according to the present embodiment will be described with reference to sequence diagrams depicted in  FIGS. 6 to 9  and timing diagrams depicted in  FIGS. 10 and 11 .  FIG. 6  depicts a switching operation of an operation mode when the microcomputers  110  and  120  included in the electronic control device  100 A make sleep requests at different timings.  FIG. 7  depicts a switching operation of an operation mode when the microcomputers  110  and  120  included in the electronic control device  100 A make sleep requests at the same timing.  FIG. 8  depicts a return operation returning from the power saving mode to the normal operation mode when a control signal is input in the first microcomputer  110 .  FIG. 9  depicts a return operation returning from the power saving mode to the normal operation mode when the communication bus driver  130  receives a signal transmitted by any one of the other electronic control devices  100 B to  100 M. 
     As depicted in  FIG. 6 , when, for instance, the first microcomputer  110  (microcomputer M1) makes a sleep request in accordance with changes in the condition of the vehicle C ( FIG. 10 : point in time t1), data frame indicative thereof is transmitted to the second microcomputer  120  (microcomputer M2), the communication bus driver  130  and the other electronic control devices  100 B to  100 M. Then, the standby terminal  112  of the first microcomputer  110  is changed to the high impedance ( FIG. 10 : point in time t2), and the first microcomputer  110  shifts to the sleeping mode from the wake-up mode ( FIG. 10 : point in time t3). 
     Subsequently, when the second microcomputer  120  makes the sleep request ( FIG. 10 : point in time t4), data frame indicative thereof is transmitted to the first microcomputer  110 , the communication bus driver  130  and the other electronic control devices  100 B to  100 M. Then, based on the data frame transmitted from the first microcomputer  110 , the second microcomputer  120  recognizes that the first microcomputer  110  has shifted to the sleeping mode, and that the second microcomputer  120  is the microcomputer that lastly shifts to the sleeping mode in the electronic control device  100 A. The second microcomputer  120  changes the logic level of the standby terminal  122  of the second microcomputer  120  from “H” to “L” ( FIG. 10 : point in time t5), and the second microcomputer  120  shifts to the sleeping mode from the wake-up mode ( FIG. 10 : point in time t6). 
     Subsequently, when the communication bus driver  130  detects that the logic level of the standby terminal  122  of the second microcomputer  120  is changed to “L”, the communication bus driver  130  shifts to the sleeping mode from the wake-up mode ( FIG. 10 : point in time t7). By this operation, the operation mode of the electronic control device  100 A shifts from the normal mode to the power saving mode. Just for reference, for instance, the logic level of the standby terminal  122  that has been changed to “L” is to be changed to the high impedance after the communication bus driver  130  shifts to the sleeping mode ( FIG. 10 : point in time t8). In this configuration, when the communication bus driver  130  having shifted to the sleeping mode shifts to the wake-up mode, the standby terminals  112  and  122  are both set to the high impedance. More specifically, this configuration suppresses the communication bus driver  130  from, irrespective of no sleep request from the microcomputers  110  and  120 , returning to the sleeping mode when the communication bus driver  130  shifts to the wake-up mode, in accordance with, for instance, the “L” logic level set to the standby terminals  112  and  122 . 
     Further, according to an example depicted in  FIG. 7 , when based on the changes in the conditions of the vehicle C, the microcomputers  110  and  120  make the sleep requests simultaneously ( FIG. 11 : point in time ta), data frame indicative thereof is transmitted to the communication lines  140 ,  141 , BS 1  and the like. In other words, the data frame indicating that the sleep request has been made is transmitted to the microcomputers  110  and  120 , the communication bus driver  130 , and the other electronic control devices  100 B to  100 M. By this operation, the microcomputers  110  and  120  each recognize that a microcomputer other than itself is making a sleep request at the same timing. Then, the microcomputers  110  and  120  respectively change the logic level of the standby terminals  112  and  122  from “H” to “L” ( FIG. 11 : point in time tb), and the microcomputers  110  and  120  shift from the wake-up mode to the sleeping mode ( FIG. 11 : point in time tc). The communication bus driver  130 , which has detected that the logic level of the standby terminals  112  and  122  of the microcomputers  110  and  120  has been changed to “L”, shifts to the sleeping mode from the wake-up mode in accordance therewith ( FIG. 11 : point in time td). In this manner, the operation mode of the electronic control device  100 A shifts to the power saving mode from the normal mode. Just for a reference, the logic level of the standby terminals  112  and  122  having been changed to “L” is to be changed to high impedance after the communication bus driver  130  shifts to the sleeping mode ( FIG. 11 : point in time te). 
     As depicted in  FIG. 8 , when the first microcomputer  110  having once shifted to the sleeping mode inputs a signal transmitted from the control target ( FIG. 10 : point in time t9), the first microcomputer  110  switches the standby terminal  112  from the high impedance to “H” ( FIG. 10 : point in time t10). Then, the first microcomputer  110  having been in the sleeping mode shifts to the wake-up mode ( FIG. 10 : point in time t11). 
     When detecting that the logic level of the standby terminal  112  of the first microcomputer  110  has been changed to “H”, the communication bus driver  130  shifts from the sleeping mode to the wake-up mode ( FIG. 10 : point in time t12). In addition, the communication bus driver  130  changes the logic level of the wake-up terminal  133  of the communication bus driver  130  from “H” to “L” ( FIG. 10 : point in time t13). 
     Then, when the logic level of the wake-up terminal  133  of the communication bus driver  130  is changed to “L”, a signal indicating this logic level is input in the wake-up terminal  123  of the second microcomputer  120  having been in the sleeping mode ( FIG. 10 : point in time t14). As the result, the standby terminal  122  of the second microcomputer  120  is changed from the high impedance to the “H” logic level ( FIG. 10 : point in time t15), and the microcomputer  120  shifts to the wake-up mode ( FIG. 10 : point in time t16). 
     On the other hand, assume that as depicted in  FIG. 9 , the bus level of the communication line BS 1 , to which the communication bus driver  130  is connected, has changed in accordance with the transmission of the signal from any one of the other electronic control devices  100 B to  100 M ( FIG. 11 : point in time tf). Then, the logic level of the standby terminal  132  of the communication bus driver  130  is changed from “L” to “H” in accordance therewith ( FIG. 11 : point in time tg), and the communication bus driver  130  having been in the sleeping mode shifts to the wake-up mode ( FIG. 11 : point in time th). 
     Subsequently, the logic level of the wake-up terminal  133  of the communication bus driver  130  having shifted to the wake-up mode is changed from “H” to “L” ( FIG. 11 : point in time ti), and the signal indicating this logic level is input in the wake-up terminals  113  and  123  of the microcomputers  110  and  120  ( FIG. 11 : point in time tj). Then, in accordance therewith, the standby terminals  112  and  122  of the microcomputers  110  and  120  are changed from the high impedance to the “H” logic level in accordance therewith ( FIG. 11 : point in time tk), and the microcomputers  110  and  120  having been in the sleeping mode shift to the wake-up mode ( FIG. 11 : point in time tl). 
     According to the electronic control device and the method of controlling the microcomputers in the present embodiment as described above, the following advantages are obtained. 
     (1) In the power saving mode provided to the electronic control device, during which the power consumed by the electronic control devices  100 A to  100 M is reduced, the microcomputers  110  and  120  having made the sleep requests are switched to the sleeping mode, and the communication bus driver  130  is also switched to the sleeping mode after all of the microcomputers included in the electronic control device  100 A have shifted to the sleeping mode. Accordingly, until all of the microcomputers included in the electronic control device  100 A have shifted to the sleeping mode, the microcomputers  110  and  120  having been in the wake-up mode are capable of continuously transmitting and receiving the signal through the communication bus driver  130 . Further in the above embodiment, in order to switch the microcomputers  110  and  120  and the communication bus driver  130  to the sleeping mode, there is no need to provide between the communication bus driver  130  and the microcomputers  110  and  120  a control circuit adapted to control the operation conditions of the microcomputers  110  and  120  and the signals transmitted from the microcomputers  110  and  120 . Therefore, configurations of the electronic control device  100 A having the microcomputers  110  and  120  and the electronic control devices  100 B to  100 M are further simplified. In this manner, with a simplified configuration, the power consumed by the microcomputers  110  and  120  is reduced while smoothly transferring the signals. 
     (2) The microcomputers  110  and  120  are provided respectively with the standby terminals  112  and  122  whose conditions are selectively set to “H” logic level, “L” logic level or high impedance in relation to the communication bus driver  130 . Further, when either one of the standby terminals  112  and  122  of the microcomputers  110  and  120  is set to the “L” logic level, the communication bus driver  130  is switched to the sleeping mode. Then, at the time of shifting to the power saving mode, the standby terminals  112  and  122  of the microcomputers  110  and  120  shifting to the sleeping mode are set to the high impedance. This configuration suppresses the communication bus driver  130  from shifting to the sleeping mode in accordance with the setting of the standby terminals  112  and  122  to the high impedance. Accordingly, without affecting the operation conditions of the communication bus driver  130  at all, either one of the microcomputers  110  and  120  is switched to the sleeping mode. 
     (3) At the time of shifting to the power saving mode, the standby terminal  112  of the first microcomputer  110 , which is the microcomputer that has made the first sleep request, is changed to the high impedance, and thereafter the standby terminal  122  of the second microcomputer  120 , which is the microcomputer that lastly shifts to the sleeping mode, is changed to the “L” logic level. Therefore, the operation conditions of the communication bus driver  130  are reliably maintained until the standby terminal of the second microcomputer  120  (i.e., the microcomputer that lastly shifts to the sleeping mode) is changed to the “L” logic level, and the communication by way of the communication bus driver  130  is reliably maintained. Accordingly, by utilizing the logic levels and conditions settable to the standby terminals  112  and  122  of the microcomputers  110  and  120 , the operation conditions of the communication bus driver  130  are reliably controllable. 
     (4) At the time of shifting to the power saving mode, if the microcomputers  110  and  120  shift to the sleeping mode simultaneously, the standby terminals  112  and  122  of the microcomputers  110  and  120  are changed to the “L” logic level simultaneously as the special exception. Therefore, if the microcomputers  110  and  120  shift to the sleeping mode simultaneously, the standby terminals  112  and  122  of the microcomputers  110  and  120  are collectively changed to the “L” logic level. Accordingly, even if the microcomputers  110  and  120  shift to the sleeping mode simultaneously, the communication bus driver  130  shifts to the sleeping mode in accordance with the shifting of the microcomputers  110  and  120  to the sleeping mode. 
     (5) The microcomputers  110  and  120  are connected with each other by the dedicated communication line  140 , and the microcomputers  110  and  120  are each configured to monitor the other one of microcomputers  110  and  120  sharing the same communication bus driver  130  based on the information received via the dedicated communication line  140 . In addition, the microcomputers  110  and  120  determine whether their standby terminals  112  and  122  are set to the high impedance or to the “L” logic level at the time of shifting to the sleeping mode, based on the operation conditions monitored. Therefore, the microcomputers  110  and  120  are capable of constantly monitoring whether or not the other microcomputers  120  and  110  sharing the same communication bus driver  130  have shifted to the sleeping mode, and also capable of determining based on the monitoring results whether their standby terminals  112  and  122  are set to the high impedance or to the “L” logic level when the microcomputers  110  and  120  shift to the sleeping mode. Accordingly, the conditions of the standby terminals  112  and  122  of the microcomputers  110  and  120  are accurately determined, and the operation conditions of the communication bus driver  130 , which is adapted to shift to the sleeping mode in accordance with the conditions of the standby terminals, are more accurately controllable. 
     (6) When the signal is input in the first microcomputer  110  from the control target of the first microcomputer  110 , the sleeping mode of the first microcomputer  110  is cancelled. In addition, when the communication bus driver  130  receives a signal from any one of the electronic control devices  100 B to  100 M (i.e., electronic control device other than the electronic control device  100 A having been in the sleeping mode), the power saving mode of the electronic control device  100 A having been in the sleeping mode is cancelled. Therefore, until various controls by the microcomputers  110  and  120  (i.e., microcomputers included in the electronic control device  100 A) become necessary, the sleeping mode of the microcomputers  110  and  120  is maintained. On the other hand, when the various controls by the microcomputers  110  and  120  become necessary, the sleeping mode of the microcomputers  110  and  120  is cancelled, and thereafter the microcomputers  110  and  120  perform the controls as required to do. Accordingly, the electronic control devices  100 A and  100 B to  100 M retain the demanded functions while retaining the time necessary for shifting to the power saving mode and reducing the power consumption. 
     (7) At the time of cancelling the power saving mode, based on the input of the signal from the control target that the first microcomputer  110  controls, the sleeping mode of the microcomputer  110  into which the signal is input is cancelled. Subsequently, the sleeping mode of the communication bus driver  130  and the sleeping mode of the second microcomputer  120  into which no signal is input from the control target are cancelled. Therefore, once the signal is input into the first microcomputer  110  from the control target, the sleeping modes of the first microcomputer  110 , the communication bus driver  130  and the second microcomputer  120  are suitably cancelled, so that various controls are performed based on the signal input from the control target. Accordingly, while the sleeping modes of the microcomputers  110  and  120  are cancelled at the right timing, the microcomputers  110  and  120  whose sleeping modes have been cancelled smoothly perform the various controls. 
     (8) At the time of cancelling the power saving mode of the electronic control device  100 A, based on the input of the signal transmitted from any one of the electronic control devices  100 B to  100 M (i.e., electronic control device other than the electronic control device  100 A), the sleeping mode of the communication bus driver  130  is cancelled. Subsequently, the sleep modes of the all of the microcomputers  110  and  120  are cancelled. Therefore, when the voltage is changed in the BS communication line BS 1  due to the signal transmitted from the other electronic control devices  100 B to  100 M, the sleep modes of the communication bus driver  130  and the microcomputers  110  and  120  included in the electronic control device  100 A are suitably cancelled, and the electronic control device  100 A performs various controls in accordance with the signal input from the control target. Accordingly, while the sleeping modes of the microcomputers  110  and  120  are cancelled at a right timing, the microcomputers  110  and  120  whose sleeping modes are cancelled more smoothly perform the various controls. 
     (9) As the electronic control device, the electronic control devices  100 A to  100 M, which are adapted to transmit and receive signals via the vehicle network installed in the vehicle C, are exemplified. Therefore, the shifting to the sleeping mode of the microcomputers  110  and  120  included in the electronic control devices  100 A to  100 M, and the cancelling of the sleeping mode of the same are also applicable to the electronic control devices  100 A to  100 M installed in the vehicle C. Accordingly, while the power consumption of the electronic control devices  100 A to  100 M is reduced, various signals are smoothly exchanged via the shared communication bus driver  130 . 
     The embodiment described above may be modified as follows. 
     At the time of shifting to the power saving mode, the logic level of the standby terminals  112  and  122 , which has been changed to “L”, is changed to the high impedance after the communication bus driver  130  shifts to the sleeping mode. However, the configuration is not limited thereto, and as long as the operation of the communication bus driver  130  after cancelling the power saving mode is secured, the logic level of the standby terminals  112  and  122  may be maintained to be continuously “L”. 
     At the time of cancelling the power saving mode of the electronic control device  100 A, the sleeping mode of the communication bus driver  130  is cancelled based on the input of a signal from any one of the electronic control devices  100 B to  100 M (i.e., electronic control device other than the electronic control device  100 A). Then, the sleep modes of all the microcomputers  110  and  120  are cancelled simultaneously. However, the configuration is not limited thereto, and after the sleeping mode of the communication bus driver  130  is cancelled, the sleeping modes of the microcomputers  110  and  120  may be sequentially cancelled. Alternatively, after the sleeping mode of the communication bus driver  130  is cancelled, the sleeping modes of the microcomputers  110  and  120  may be cancelled after lapse of a predetermined time. 
     At the time of cancelling the power saving mode, based on the input of the signal from the control target that the first microcomputer  110  controls, the sleeping mode of the microcomputer  110  into which such signal is input is cancelled. Subsequently, the sleeping mode of the communication bus driver  130 , and the sleeping mode of the second microcomputer  120  into which no signal is input from the control target are cancelled. The sleeping mode of the second microcomputer  120  may be likewise configured to, when a signal is input from the control target that the second microcomputer  120  controls, be cancelled based on the input of such signal. Then, the sleeping mode of the communication bus driver  130  and the sleeping mode of the microcomputer  110  into which no signal is input from the control target may be configured to be cancelled. Further, the electronic control device may employ a configuration where: the sleeping mode of the first microcomputer  110  is cancelled when inputting a signal from the control target that the microcomputer  110  controls; and the sleeping mode of the second microcomputer  120  is cancelled when inputting a signal from the control target that the second microcomputer  120  controls. In addition to the above, the electronic control device may set as desired the process and timing for switching the sleeping microcomputers  110  and  120  and the communication bus driver  130  to the wake-up modes. 
     When a signal is input from the control targets that the microcomputers  110  and  120  control, the sleeping modes of the microcomputers  110  and  120  are cancelled. Further, when the communication bus driver  130  receives a signal transmitted from any one of the electronic control devices  100 B to  100 M (i.e., electronic control device other than the sleeping electronic control device  100 A), the power saving mode of the electronic control device  100 A, which is in the sleeping mode, is cancelled. However, the configuration is not limited thereto, and for instance, the microcomputers  110  and  120  or the electronic control device  100 A may input a signal indicating of the changes in the vehicle conditions of the vehicle C, and the sleeping modes of the microcomputers  110  and  120  and the communication bus driver  130  may be cancelled based on such input signal. Alternatively, for instance, the sleeping modes of the microcomputers  110  and  120  and the communication bus driver  130  may be configured to be cancelled upon the lapse of a predetermined time after any one of the microcomputers  110  and  120  and the communication bus driver  130  has shifted to the sleeping mode. 
     The microcomputers  110  and  120  are connected with each other by the dedicated communication line  140 , and the microcomputers  110  and  120  are each controlled to monitor the other one of the microcomputers  110  and  120  sharing the same communication bus driver  130 , based on the information transmitted through the dedicated communication lines  140 ,  142  and  143 . However, the configuration is not limited thereto, and any configuration may be employed as long as the microcomputers  110  and  120  are capable of receiving the data frame transmitted from the microcomputers  120  and  110 . For instance, the communication bus driver  130  may be configured to transmit the data frame transmitted from the microcomputers  110  and  120 , and the data frame received by the communication bus driver  130  may be transferred to the microcomputers  120  and  110  from the communication bus driver  130 . Likewise, the communication bus driver  130  may be configured to monitor the operation conditions of the microcomputers  110  and  120 , and to transmit from the communication bus driver  130  the signal indicating of the monitor results to the microcomputers  120  and  110 . 
     When the microcomputers  110  and  120  make the sleep requests simultaneously, the standby terminals  112  and  122  of the microcomputers  110  and  120  are switched to the “L” logic level simultaneously. However, the configuration is not limited thereto, and if the microcomputers  110  and  120  make the sleep requests simultaneously, either one of the standby terminals  112  and  122  of the microcomputers  110  and  120  may be set to the high impedance, and thereafter the other one of the standby terminals  122  and  112  may be set to the “L” logic level. 
     At the time of shifting to the power saving mode, the standby terminal  112  of the first microcomputer  110 , which has first made the sleep request, is switched to the high impedance, and thereafter the standby terminal  122  of the second microcomputer  120 , which is the microcomputer that lastly shifts to the sleeping mode, is switched to the “L” logic level. However, the configuration is not limited thereto, and any configuration is employable, as long as the communication bus driver  130  is switched to the sleeping mode after all the microcomputers  110  and  120  included in the electronic control device  100 A have shifted to the sleeping mode. The setting details of the standby terminals  112  and  122  may be suitably changed. 
     The microcomputers  110  and  120  are respectively provided with the standby terminals  112  and  122  whose conditions are selectively set to “H” logic level, “L” logic level or high impedance in relation to the communication bus driver  130 , and when either one of the standby terminals  112  and  122  of the microcomputers  110  and  120  is set to the “L” logic level, the communication bus driver  130  shifts to the sleeping mode. However, the configuration is not limited thereto, and any configuration may be employed as long as the communication bus driver  130  shifts to the sleeping mode in accordance with the shifting of both the microcomputers  110  and  120  to the sleeping mode. 
     The power saving mode is defined as a mode where the microcomputers  110  and  120  included in the electronic control device  100 A and the communication bus driver  130  are all in the sleeping mode. However, the definition is not limited thereto, and the power saving mode may be a mode where any one of: the microcomputers  110  and  120  included in the electronic control device  100 A; and the communication bus driver  130  is in the sleeping mode. 
     The electronic control devices  100 A and  100 B to  100 M are each configured to include the communication bus driver  130  and the two microcomputers  110  and  120  sharing the same communication bus driver  130 . However, the configuration is not limited thereto, and the electronic control devices  100 A and  100 B to  100 M each may be configured to include three or more microcomputers sharing the same communication bus driver  130 . Even with this configuration, when all the microcomputers included in the electronic control device have shifted to the sleeping mode, the communication bus driver  130  shifts to the sleeping mode. Thus, until all the microcomputers shift to the sleeping mode, the microcomputers in the wake-up mode are maintained to be communicable. 
     As the vehicle network, a CAN is employed. In addition to CANs, the vehicle network may be suitably modified, and may be any network as long as such network serves as the communication method for the electronic control device having the microcomputers sharing the same communicator. 
     As the electronic control device, the electronic control devices  100 A to  100 M installed in the vehicle C and adapted to control the respective control targets are employed. However, the electronic control device is not limited thereto, and the electronic control device may be any electronic control device as long as such electronic control device includes the microcomputers sharing the same communicator, such as an electronic control device installed in various information terminals or various devices and adapted to control the control targets. Even with this configuration, the microcomputers for which the sleep requests are made are switched to the sleeping mode while the microcomputers in the wake-up mode are maintained to be communicable. In this manner, the power consumption is reducible while favorably maintaining the communication function of the electronic control device. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       100 A to  100 M . . . electronic control device,  100 N . . . gateway,  110  . . . first microcomputer,  111  . . . communication controller,  112  . . . standby terminal,  113  . . . wake-up terminal,  120  . . . second microcomputer,  122  . . . standby terminal,  123  . . . wake-up terminal,  130  . . . communication bus driver,  131  . . . communication controller,  132  . . . standby terminal,  133  . . . wake-up terminal,  140 ,  141 ,  142 ,  143  . . . communication line, C . . . vehicle, BS 1  to BS 3 , BS 1   a , BS 1   b  . . . communication line