Communication system with framing error detection

Abstract: At the occurrence of a framing error in a slave unit, the cause of error is analyzed and interrupt is inhibited or enabled depending on the cause of error, whereby optimal data communication can be performed. When an interrupt request is issued, whether or not the interrupt is caused by a framing error is determined (501). With an affirmative determination result, whether or not framing errors occur twice or more continuously is determined (515). Interrupt is not inhibited (i.e., enabled) in the case of a negative determination result, or interrupt is inhibited (525) in the case of an affirmative determine result.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a communication system which performs data transmission and reception between a master unit (e.g., an external unit such as a tester) and slave units (e.g., electronic control units such as an engine controller). 2. Description of Related Art: There is known a communication system for the transmission and reception of data between a master unit and slave units as shown in Fig. 9, in which a master unit 100 and slave units 110-130 are connected through a communication line 140 and connection means 150, and the slave units 110-130, which have received a request message sent by the master unit 100 over the communication line 140, send response messages for the request message over the communication line 140 sequentially in the order of priority of the slave units 110-130. The arrangement of the system shown in Fig. 9 will be explained in brief. The first slave unit 110 includes a CPU 111 that is used mainly for communication and a CPU 112 that is used mainly for control. The CPU 111 is connected with a communication I/O device 113 which can monitor request messages from the master unit 100 and response messages from other slave units 120 and 130, and the CPU 112 is connected with a control I/O device 114 used for control. The CPU 111 and CPU 112 are connected together by a data bus 115. The CPU 111 incorporates a serial interface (S.I.) 116 which facilitates the serial communication, a RAM 117, a ROM 118, etc. The other slave units 120 and 130 have the same internal arrangement as the first slave unit 110. The request message and response message are each formed of multiple 1-byte data (11 bytes at maximum). Each 1-byte data having a 10-bit length consists of a low-active start bit (S), eight data bits (0-7) and a high-active stop bit (P), as shown in Fig. 10. For dealing with request messages and response messages each consisting of 10-bit data, the serial interface 116 is specifically arranged as shown in Fig. 11. Based on this arrangement, serial-in data received on a serial-in terminal 201 is held by a serial status register 203 by way of a buffer 202. After the register 203 has detected the start bit (S), the successive data bits (0-7) are shifted into a serial-in shift register 204 at a prescribed baud rate. When the register 203 detects the stop bit (P), the 1-byte data consisting of 10 bits is transferred to a serial-in data register 205, and an interrupt request is generated (refer to Figs. 12A and 12B) so that the software can access to the serial-in data over a data bus 206. On the other hand, in serial-out mode, output data is written into a serial-out register 207 over the data bus 206 by the software, and the serial output operation is initiated by a controller 208. The register 207 transfers the data to a serial-out shift register 209. Initially, the start bit (S) is released from the serial-out terminal 211 by way of a buffer 210. Subsequently, the second bit (0) through the stop bit (P) are released in the same manner, and an interrupt request is issued to the software. For a communication system as described above, it is a general practice to make initialization prior to the transaction of the above-mentioned messages between the master unit 100 and slave units 110-130. This initialization generally takes place in compliance with the communication procedure stated in the international standard ISO-9141-2. The following explains in brief with reference to Figs. 13A and 13B the communication procedure based on this international standard. Initially, the master unit 100, which has confirmed that the communication line 140 has an idle time of 2 ms or more, sends out an initialization address (e.g.,33H) at a baud rate of 5 bps (bits per second) over the communication line 140. The first slave unit 100 of the highest priority confirms that the idle time becomes W1 or more, and then sends out a sync signal (e.g.,55H) at a baud rate determined by the initialization address (e.g.,10.4 kbps) over the communication line 140. Following the transmission of the sync signal, the first slave unit 110 confirms that the idle time becomes W2 or more, and then sends out a key word 1 (KW1, e.g.,94H) over the communication line 140. Following the transmission of the key word 1, the first slave unit 110 confirms that the idle time becomes W3 or more, and then sends out another key word 2 (KW2, e.g.,94H) over the communication line 140. Following the transmission of the KW2 by the first slave unit 110, the master unit 100 confirms that the idle time is W4 or more, and then sends out an inverted version of the KW2 (e.g.,6BH) over the communication line 140. Following the transmission of the inverted KW2 by the master unit 100, the first slave unit 110 confirms that the idle time is W4 or more, and then sends out an inverted version of the initialization address (e.g., CCH) over the communication line 140. On completion of transmission of this inverted signal, the initialization process completes. The other slave units 120 and 130 implement their own initialization process against the master unit 100 and first slave unit 110 by monitoring signals on the communication line 140 with their own I/O devices. The above-mentioned W1 through W4 are set arbitrarily within the respective ranges stated in the international standard, which are specifically 60-300 ms for W1, 5-20 ms for W2, 0-20 ms for W3, and 25-50 ms for W4. On completion of initialization, the transaction (transmission/reception) of a request message and response messages begins between the master unit 100 and slave units 110-130 at the baud rate determined by the initialization address (10.4 kbps in this example). This message transaction takes place also in compliance with the international standard. This communication procedure will be explained in brief with reference to Figs. 14A-14D. Initially, when the master unit 100 sends a request message 1 (Fig. 14A) for requesting the execution of certain processes by the slave units 110-130 over the communication line 140, the first slave unit 110 of the highest priority sends a response message (Fig. 14B) for the request message 1 over the communication line 140 on expiration of an idle time P2 (arbitrary time period in the range from 0 to 50 ms) following the end of transmission of the request message 1. On completion of transmission of the response message by the first slave unit 110, the second slave unit 120 of the next priority confirms the expiration of the idle time P2 and then sends its own response message. Finally, on completion of transmission of the response message by the second slave unit 120, the third slave unit 130 of the lowest priority confirms the expiration of the idle time P2 and then sends its own response message (Fig. 14D). On completion of transmission of the response message by the third slave unit 130, the master unit 100 confirms the expiration of an idle time P3 (arbitrary time period in the range from 55 ms to 5 s) and then sends a next request message 2. The slave units 110-130 send their own response messages sequentially in the same manner as explained above. The international standard states that the initialization address of Fig. 13A can be sent if the idle time lasts for 2 ms or more. In the example shown in Figs. 14A-14D, the idle time P3 after the end of transmission of the response message by the third slave unit 130 until the master unit 100 begins to send the request message 2 will be 55 ms or more, and therefore the master unit 100 can possibly send the initialization address erroneously during this idle time. Namely, during the transaction of messages at a high baud rate of 10.4 kbps, the master unit 100 can possibly send the initialization address at as slow baud rate as 5 bps. In this event, each of the slave units 110-130 first takes in the start bit (low level) of the initialization address from the serial-in terminal 201 (Fig. 11) of the CPU 111, transfers the bit to the registers 204 and 205, and initiates the interrupt process. In this case, the slave units 110-130, which are operative to receive 10.4-kbps data and actually receives the 5-bps start bit, effectively receives a 1-byte data (Fig. 10) of all low-level bits about 200 times repeatedly, and consequently interrupt requests are generated about 200 times continuously. Each of the about 200 input 1-byte data has all low bits as shown in Fig. 15A1, and therefore the CPU cannot detect a correct stop bit (high level) at all interrupt events (Fig. 15A2), resulting in the emergence of framing error (Fig. 15A3: stop bit has not a correct level) at all interrupt events. Accordingly, if the master unit 100 sends the initialization address having a very low baud rate during the transaction of messages at a high baud rate, it causes the slave units 110-130 to issue a number of interrupts. Consequently, the CPU 111 executes only the interrupt process, leaving the base routine and other processing functions uncompleted, and the slave units are paralyzed. The above-mentioned problem also arises when the master unit 100 is having normal data transactions (at 10.4 kbps) with multiple slave units (e.g., all slave units 110-130) following the initialization of these slave units and if the master unit 100 initializes one of the slave units (e.g., second slave unit 120). For coping with this matter, the conventional system is provided with a detection means for detecting the occurrence of a framing error, and the interrupt process is inhibited (Fig. 15B4) on detecting the occurrence of a framing error based on the presumption that the base routine and other processing functions are precluded, as shown in Figs. 15B1-B4. However, the following problem will arise in this case. Namely, in case the foregoing communication system is used for a land vehicle for example, the CPU 111 may receive a radio wave from the transceiver or a noise from the ignition system during the message reception by the master unit 100 or slave units 110-130 and this noise may cancel the stop bit as shown in Figs. 16A-16D shown in correspondence to Figs. 15A-15D. The reception of this message by a slave unit obviously results in the creation of a framing error. The cause of framing error creation of this case differs greatly from the case of successive triggering of interrupt process as in the case of the transmission of initialization address at a very low baud rate during the transaction of a message at a high baud rate as mentioned above. However, the above-mentioned conventional scheme works to inhibit the interrupt process also in this case in response to the framing error creation, and therefore each slave unit will not be able to receive a message from the master unit 100 or other slave unit as shown in Figs. 16A-16D. When the vehicle is started during the reception of a message by the master unit 100 or slave units 110-130, the power voltage to the slave units 110-130 will fall by the starting operation, resulting possibly in the cancelling of data of the message. The stop bit of the message may be canceled, and the reception of the message obviously results in the creation of a framing error. The cause of framing error creation of this case also differs greatly from the case of successive triggering of interrupt process, and the above-mentioned conventional scheme works to inhibit the interrupt process also in this case in response to the framing error creation, and therefore each slave unit will not be able to receive a message from the master unit 100 or other slave unit. SUMMARY OF THE INVENTION The present invention is intended to deal with the foregoing problem, and its object is to provide a communication system which inhibits the interrupt process at the occurrence of a framing error, wherein the system examines the cause of framing error creation and inhibits the interrupt process thereby to allow a base routine and other processing functions to take place if the cause of framing error is to trigger a number of interrupt processes. According to the invention, a framing error detection does not inhibit an interrupt process immediately at the detection of a framing error, but the interrupt process is inhibited in response to the determination of the detection of framing errors at a high frequency. Accordingly, even if the framing error occurs, the interrupt process inhibition does not take place unless the cause of framing error creation is to generate framing errors at a high frequency, e.g., such as a case where a noise happened to cancel the stop bit, and consequently the inherent data communication based on this interrupt process can be performed effectively. In case the cause of framing error creation is to create framing errors at a high frequency, the interrupt process inhibition takes place, and in this case the base routine and other processing functions are performed on a priority basis. Preferably, it is determined whether or not the framing error is detected a certain number of times or more continuously. Thus, when framing errors occur continuously certain number of times or more, the cause of the framing errors is assumed to trigger a number of interrupt processes continuously, and the interrupt process is inhibited. Preferably, it is determined whether or not the number of times of detection of framing errors is a certain proportion or more with respect to the number of times of initiation of interrupt process. Alternatively, it is determined whether or not the number of times of detection of framing errors is a certain proportion or more with respect to a time period since the first detection of a framing error by the framing error. Preferably, the slave units are installed on a land vehicle. In this case, although framing errors may occur in slave units due to the noise or the starting of the vehicle, the interrupt process is enabled, and the inherent data communication based on the interrupt process can be performed effectively. According to the invention, in a slave unit, an interrupt process inhibition does not take place in case the cause of framing error creation is not to create framing errors at a high frequency, allowing inherent data communication based on the interrupt process to take place effectively. The interrupt process inhibition takes place in case the cause of framing error creation is to create a number of interrupt processes continuously, allowing the base routine and other processing functions to take place on a priority basis. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is an overall block diagram of the first embodiment of this invention; Fig. 2 is a flowchart showing the initialization address reception process carried out by each controller of the first embodiment; Fig. 3 shows the subroutine of step 305 of Fig. 2; Fig. 4 is a flowchart showing the base routine carried out by each controller of the first embodiment; Fig. 5 is a flowchart showing the serial-input interrupt process carried out by each controller of the first embodiment; Figs. 6A-6D are timing charts of the signals at the reception of the 5-bps initialization address during the wait state of the CPU for data reception at 10.4 kbps according to the first embodiment; Fig. 7 is a flowchart showing the serial-input interrupt process carried out by each controller of the second embodiment of this invention; Fig. 8 is a flowchart showing the serial-input interrupt process carried out by each controller of the third embodiment of this invention; Fig. 9 is an overall block diagram of the conventional communication system; Fig. 10 is a timing chart showing the bit format of 1-byte data. Fig. 11 is a block diagram showing the internal arrangement of the serial interface 116 of the system shown in Fig. 9; Figs. 12A and 12B are timing charts of the signals at the input of serial-in data to the CPU; Figs. 13A and 13B are timing charts of the signals transacted between the master unit and a slave unit during the initialization process; Figs. 14A-4D are timing charts showing the transmission procedure of the request message and response message transacted between the master unit and slave units; Figs. 15A1-15A3 are timing charts of the signals at the reception of the 5-bps initialization address during the communication at 10.4 kbps by the CPU, and Figs. 15B1-15B4 are timing charts of the same signals in Figs. 15A1-15A3 of the case when interrupt is inhibited in response to the detection of a framing error; and Figs. 16A-16D are timing charts of the signals when a framing error occurs due to a noise. DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS The present invention will be described with reference to various embodiments illustrated in the accompanying drawings. The first embodiment of this invention illustrated in Figs. 1 through 5 is applied to a diagnostic system for a land vehicle. The system of this embodiment includes a plurality of electronic controllers (engine controller 1, transmission controller 2, etc.) as slave units installed on the vehicle and an externally-connected fault diagnostic tester 5 as a master unit connected through a communication line 3 and a diagnostic connector 4, and data communication takes place between the fault diagnostic tester 5 and individual electronic controllers in 1-to-n relationship. The electronic controllers are given in advance the priority order for carrying out the 1-to-n data communication, and when the fault diagnostic tester 5 sends a request message for requesting the execution of certain processes of the electronic controllers over the communication line 3, the electronic controllers returns their response messages sequentially in the order of priority over the communication line 3. Specifically, in this embodiment, the priority order is set such that the transmission controller 2 has the higher priority over the engine controller 1. It is assumed that the communication between the fault diagnostictester 5 and the vehicle-installed electronic controllers is based on the protocol which complies with the international standard (ISO-9141-2). The following explains the structure and function of the engine controller 1 as an example of the vehicle-installed electronic controllers. The engine controller 1 includes a CPU 11, ROM 12, RAM 13, input circuit 14, output circuit 15, A/D converter 16, and communication circuit 17. The communication circuit 17 is an input/output buffer circuit which drives the communication line 3. The input circuit 14 receives sensor signals, which are mainly pulse signals, produced by a sensor 21 for detecting the number of revolutions of the engine (specifically the crank angle sensor) and a sensor 22 of the vehicle speed, and the A/D converter 16 receives sensor signals, which are analog signals, produced by a throttle sensor 23, air flow meter 24, water temperature sensor 25 and oxygen sensor 26 disposed in various sections of the vehicle. These signals are stored as sensor data of detected values in the data area of the RAM 13, and the data are used by the CPU 11 for the calculation of the amount of fuel injection and timing of ignition. The RAM 13 has areas used for the counters, buffers and flag registers besides the data area, as will be explained later. The CPU 11 implements the prescribed computations for the sensor data stored in the RAM 13 in accordance with control programs which are stored in advance in the ROM 12, thereby determining the fuel injection value and ignition timing, and also the transaction (i.e., transmission/reception) of communication messages with the fault diagnostictester 5 as will be explained later and the diagnostic processes specified by the messages. The control programs stored in the ROM 12 include a counter program which carries out the counting on a software basis for the counters in the RAM 13. The fuel injection value computed by the CPU 11 is fed to the output circuit 15, which delivers a signal representing the amount of fuel injection to an engine control means 27. The engine control means 27 is a fuel injection valve for example. The CPU 11 incorporates a serial interface (not shown) which facilitates the serial communication, and the serial interface has an internal arrangement shown in Fig. 11. The fault diagnostictester 5 is arranged to include a CPU, ROM, RAM, communication circuit, etc. as in the case of the electronic controller explained above. The fault diagnostictester 5 has its diagnostic mode set by the inspector on an operation means 5a (specifically a keyboard) provided on the external surface of the fault diagnostictester 5, and a request message which depends on the diagnostic mode is sent through the diagnostic connector 4 to the electronic controllers. The fault diagnostictester 5 is capable of informing the result of diagnosis to the inspector by listing or graphically displaying the content of response message for the request message on a display device (not shown). The diagnostic connector 4 is supplied with electric power from a battery 19 by way of an ignition switch 18 so that power is supplied to the fault diagnostictester 5 through the diagnostic connector 4 when thetester 5 is coupled electrically to the vehicle-installed electronic controllers. The vehicle communication system arranged as explained above carries out the initialization process for the fault diagnostictester 5 and electronic controllers prior to the message transaction between the fault diagnostictester 5 and electronic controllers. The initialization process has been explained in connection with Fig. 13, and explanation is not repeated here. Following the initialization process, the message transaction takes place between the fault diagnostictester 5 and electronic controllers. The message transaction has been explained in connection with Fig. 14, and explanation is not repeated. Next, the initialization process and response message transmission process carried out by each electronic controller will be explained in detail with reference to Fig. 2 through Fig. 5. The counters, buffers and flag registers used in the processes explained in the following are all initialized to "0" when the ignition switch 18 is turned on and power is supplied to the electronic controllers. Initially, an interrupt routine of Fig. 2 is initiated at a 2-ms interval so as to receive the initialization address (Fig. 13A) sent by the fault diagnostic tester 5 at 5 bps (200 ms for one bit). Step 300 of the routine determines whether or not data is loaded in address data buffers (1) through (10), which will be explained later, thereby to determine as to whether or not the reception of initialization address has completed. If the step 300 detects the incompletion of initialization address reception, i.e., the absence of data in the address data buffers (1) through (10), the sequence at step 305 branches to a subroutine shown in Fig. 3 for the preparation of the reception of 1-bit data of the initialization address. Specifically, the first step 350 increments an address reception counter CT2M, and the next step 355 determines whether or not the communication line 3 is in a state of high level (H). If the communication line 3 is detected to be of high level, the next step 360 increments a counter CBUSH which counts the number of times of detection of the high-level communication line 3, and the sequence proceeds to step 365, or otherwise on detecting the communication line 3 to be of low level, the sequence proceeds intact to step 365. The step 365 determines whether or not the counter CT2M has reached 100, thereby determining whether or not the all 1-bit data of the initialization address have been received. In the case of a negative determine result, indicative of the incompletion of reception of the 1-bit data, the sequence goes out of this routine intact. Otherwise, in the case of an affirmative determine result, indicative of the completion of reception of all 1-bit data, the next step 370 clears the counter CT2M, thereby preparing for the reception of the next 1-bit data. The next step 375 determines whether or not the counter CBUSH has reached a certain number (50 in this embodiment). In the case of an affirmative determine result, indicative of the reception of high-level 1-bit data, the next step 380 sets high-level "1" to an address data buffer (m). Subsequently, step 390 clears the counter CBUSH, thereby preparing for the reception of the next 1-bit data, and the sequence goes out of this subroutine. Otherwise, in the case of a negative determine result, indicative of the reception of low-level 1-bit data, step 385 sets low-level "0" to the address data buffer (m). Subsequently, the step 390 clears the counter CBUSH, and the sequence goes out of this subroutine. The process of step 305 (Fig. 2) is repeated until data of initialization address is set in all address data buffers (1) through (10), resulting in an affirmative determine result of the step 300, and then the process of step 310 is carried out. The step 310 sets the interrupt mask flag thereby to enable the serial-in interrupt process (SIN interrupt process), and resets a flag XFRERR. The flag XFRERR, which will be explained later in connection with Fig. 5, is set when a framing error has occurred. Each electronic controller has individual base routine as shown in Fig. 4, besides the processes of Fig. 2 and Fig. 3. Step 400 of this routine determines whether or not the initialization address is set in the address data buffers (1) through (10) thereby to detect whether or not the reception of the initialization address has completed. On detecting the incompletion, the sequence goes out of this process intact. Otherwise, on detecting the completion of reception of the initialization address in step 400, the next step 405 determines whether or not the initialization process has entirely completed by determining whether or not the transmission of the inverted initialization address of Fig. 13 has completed. On detecting the incompletion, the sequence branches to the subroutine of step 410. The step 410 searches the ROM 12 for the idle time (W1-W4) for the signal to be sent among the sync signal, KW1, KW2 and inverted signal of initialization address. For example, when the sync signal is about to be sent, the step 410 searches the ROM 12 for the time W1. The next step 415 determines whether or not the idle counter which counts the idle time is greater than or equal to the idle time that had been retrieved in step 410. In the case of an affirmative determine result, the next step 420 transmits the signal, and the sequence goes out of the routine, or otherwise in the case of a negative determine result, the sequence goes out of the routine intact. The idle counter is up-counted by one at each event of time interrupt (e.g.,4-ms interrupt) based on a timer (not shown). The step 410 includes a determine step for determining whether or not the inverted KW2 signal from the fault diagnostictester 5 has been received. On the other hand, if the step 405 detects the completion of entire initialization process, the next step 425 determines whether or not a request message from the fault diagnostictester 5 has been received. In the case of the determination of receiving no request message, the sequence goes out of the routine intact, or in the case of the determination of receiving a request message, the sequence branches to a subroutine of step 430 thereby to generate a response message for the request message. The next step 435 searches the ROM 12 for the idle time P2 (24 ms in this embodiment) needed for the transmission of this response message, and the next step 440 determines whether or not the idle counter is greater than or equal to the retrieved idle time P2. In the case of an affirmative determine result, step 445 transmits the response message, and the sequence goes out of the routine. On completion of reception of the initialization address, each electronic controller enters the state of serial communication at 10.4 kbps. The serial communication takes places in the SIN interrupt process shown in Fig. 5, and it will be explained in the following. The SIN interrupt process is triggered by a serial-in interrupt to the CPU. Specifically, the SIN interrupt of step 500 is issued at each reception of the inverted KW2 signal or 1-bit data of request message from the fault diagnostictester 5, or the sync signal, KW1, KW2, inverted initialization address signal or 1-bit data of response message from other electronic controller. The next step 505 determines whether or not this SIN interrupt process has been triggered by overrun error based on the overrun error flag which is set at the occurrence of an overrun. The overrun error signifies that when the serial-in terminal 201 of Fig. 11 receives 10-bit serial data and the data is transferred to the register 204, another data is already loaded in the data destination register 205. In case the step 505 determines the SIN interrupt process to be triggered by overrun error, the sequence branches to the subroutine of step 510 thereby to carry out the process for the occurrence of SIN error (e.g., clearing of the serial data buffer for loading the SIN data). The next step 560 clears the SIN interrupt request flag, thereby preparing the acceptance of SIN interrupt of the next byte data. The SIN interrupt request flag, which records the acceptance of an interrupt request, is set on a hardware basis when an interrupt request is issued. In case the step 505 determines that this SIN interrupt process has not been triggered by overrun error, step 515 determines whether or not this SIN interrupt process has been triggered by framing error based on the framing error flag which is set at the occurrence of a framing error. The framing error signifies that the stop bit is not a correct value. In case the step 515 determines the SIN interrupt process to be triggered by framing error, step 520 determines whether or not the flag XFRERR is set, thereby determining whether or not framing errors have occurred twice or more continuously. In the case of a negative determine result, i.e., if the framing error is determined to be the first one, step 535 sets the flag XFRERR, and after the processes of steps 510 and 560 are carried out, the sequence goes out of this routine. In the case of an affirmative determine result of step 520, indicative of the occurrence of framing errors twice or more continuously, step 525 resets the interrupt mask flag thereby to inhibit the SIN interrupt process by blocking another SIN interrupt request from entering the CPU and prepare for the reception of initialization address. Consequently, the process of Fig. 2 takes place continuously without suspension. Step 530 clears the address data buffers (1) through (10) so that the step 300 of Fig. 2 makes a negative determine result. Subsequently, the processes of steps 510 and 560 are carried out, and the sequence goes out of this routine. On the other hand, if the step 515 determines that the SIN interrupt process has not been triggered by framing error, step 540 resets the flag XFRERR, and the sequence branches to a subroutine of step 545 to carry out the process for loading the SIN data into the serial data buffer. Finally, the process of step 560 is carried out. In this embodiment as described above, when the step 515 detects the occurrence of a framing error, the step 520 further determines whether or not framing errors occur twice or more continuously, and the step 525 inhibits the SIN interrupt process only in the case of the determination that framing errors have occurred twice or more continuously. Otherwise, when framing errors have not occurred twice or more continuously, the step 540 resets the flag XFRERR to keep the SIN interrupt process enabled, which is based on the following reason. Possible cases of an affirmative determine result of step 515 include the reception of the 5-bps initialization address during the state of waiting of the CPU for 4-kbps data reception, and the reception of the CPU 11 of a faulty stop bit of data canceled by a radio wave from the transceiver or a noise from the ignition system. In the former case, a number of framing errors occur continuously, resulting in an affirmative determine result of step 520. Therefore, the base routine and other processes do not go on unless the SIN interrupt process is inhibited. On this account, the step 530 inhibits the SIN interrupt process so that the base routine and other processes take place on a priority basis according to this embodiment. In the latter case, it is fairly conceived that the incident of stop bit cancelage by a noise will not occur twice or more continuously. Accordingly, the step 515 in the next cycle will make a negative determine result. Based on this presumption, in this embodiment, the step 540 resets the flag XFRERR to retain the SIN interrupt process enabled so that the inherent data communication based on the SIN interrupt can take place. In this embodiment, the step 525 inhibits the SIN interrupt process at the reception of the 5-bps initialization address during the state of waiting of the CPU 11 for 4-kbps data reception, as in the former case. However, at the time of completion of initialization address reception, the step 300 of Fig. 2 makes an affirmative determine result, which is followed by the process of step 310, and the SIN interrupt process can resume. Figs. 6A-6D show timing charts of the data signal on the data bus (Fig. 6A), interrupt request signal (Fig. 6B), framing error signal (Fig. 6C) and interrupt inhibit signal (Fig. 6D) at the time of reception of the 5-bps initialization address during the wait state of the CPU 11 for 10.4-kbps data reception. Next, the second and third embodiments of this invention will be explained for only portions different from the foregoing first embodiment. The second and third embodiments are based on the following facts (1) and (2). (1) Normally, when the 5-bps initialization address is received during the serial communication at 10.4 kbps, framing errors occur continuously as described above. However, these framing errors may not occur continuously in the presence of external noises during the reception of initialization address. (2) It is fairly conceived that the incident of external noise attack during the initialization address reception will not arise a number of times continuously. Based on these facts (1) and (2), the second embodiment is designed to inhibit the SIN interrupt process when the number of times of occurrence of framing errors is a certain proportion or more with respect to the number of times of triggering of SIN interrupt process. The third embodiment is designed to inhibit the SIN interrupt process when the number of times of occurrence of framing errors is a certain proportion or more during a certain time period since the first occurrence of framing error. Namely, the second and third embodiments are designed to inhibit the SIN interrupt process when framing errors occur at a high frequency even if the occurrence of framing errors is not continuous. Specific method of carrying out the second and third embodiments will be explained in connection with Fig. 7 and Fig. 8, respectively. Processing steps identical to those of the first embodiment (Fig. 5) are referred to by the same reference numerals, and explanation thereof is omitted. In the second embodiment shown in Fig. 7, the SIN interrupt process of step 500 is initiated at each reception of the inverted KW2 signal or 1-bit data of request message from the fault diagnostictester 5 or the sync signal, KW1, KW2, inverted initialization address signal or 1-bit data of response message from other electronic controller. The next step 501 increments a counter CSIN which counts the number of times of triggering of the SIN interrupt process. Subsequently, when step 505 makes an affirmative determine result, the process of step 510 is carried out, or the sequence proceeds to determination step 515 for a negative determine result. In the case of an affirmative determine result of step 515, step 521 increments a counter CFRMER which counts the number of times of occurrence of framing errors, and the process of step 510 is carried out. Otherwise, if the step 515 makes a negative determine result, the process of step 545 is carried out. The next step 546 determines whether or not the counter CFRMER becomes greater than or equal to a certain number (3 in this embodiment). In the case of an affirmative determine result, indicative of the occurrence of framing errors at a high frequency, the following steps 547 and 548 carry out the same processes as the steps 525 and 530 of Fig. 5. Steps 550 and 551 clear the counters CSIN and CFRMER, and following the process of step 560, the sequence goes out of this routine. On the other hand, if the step 546 makes a negative determine result, the next step 549 determines whether or not the counter CSIN becomes greater than or equal to a certain number (5 in this embodiment). In the case of a negative determine result, the process of step 560 is carried out, and the sequence goes out of this routine. In another case of an affirmative determine result, the processes of steps 550, 551 and 560 are carried out, and the sequence goes out of this routine. In the second embodiment, as described above, the SIN interrupt process is inhibited if the number of times of occurrence of framing errors with respect to the number of times of triggering of the SIN interrupt process is a certain proportion or more (three framing errors with respect to five events of SIN interrupt process in this embodiment), and consequently the SIN interrupt process can be inhibited even in the event of an external noise attack during the reception of initialization address In the third embodiment shown in Fig. 8, the SIN interrupt process of step 500 is initiated at each reception of the inverted KW2 signal or 1-bit data of request message from the fault diagnostictester 5 or the sync signal, KW1, KW2, inverted initialization address signal or 1-bit data of response message from other electronic controller. If a determination process of the step 505 makes an affirmative determine result, the process of step 510 is carried out, or the process of step 515 is carried out for a negative determine result. If the step 515 makes a negative determine result, the process of step 545 is carried out, or the process of step 521 is carried out for an affirmative determine result. Following the process of step 521, the next step 522 determines whether or not the counter CFRMER is "1", thereby determining whether or not the framing error is of the first occurrence. If the step 522 makes an affirmative determine result, the next step 523 clears a counter CTSIN which counts the time expiration since the first occurrence of framing error, and the process of step 510 is carried out. Otherwise, if the step 522 makes a negative determine result, the sequence proceeds intact to the process of step 510. The counter CTSIN is up-counted by one at each event of timer interrupt (2-ms interrupt). If the determination of the step 546 makes an affirmative determine result, the processes of steps 547 and 548 are carried out. Steps 553 and 554 clear the counters CSIN and CTSIN, and following the process of step 560, the sequence goes out of this routine. On the other hand, if the step 546 makes a negative determine result, step 552 determines whether or not the counter CSIN becomes greater than or equal to a certain time period (20 ms in this embodiment). In the case of a negative determine result, the process of step 560 is carried out, and the sequence goes out of this routine. In another case of an affirmative determine result, the processes of steps 553, 554 and 560 are carried out, and the sequence goes out of this routine. In this embodiment, as described above, the SIN interrupt process is inhibited if the number of times of occurrence of framing errors is a certain proportion (3 times) or more within a certain time period (20 ms) since the first occurrence of framing error, and consequently the SIN interrupt process can be inhibited even in the event of an external noise attack during the reception of initialization address. In addition, the present invention may be modified in the following manner. In the routine of Fig. 3, the processes of steps 355 and 360 may be altered to load data that is being received currently into a reception buffer (n), with the determination of step 375 being altered to determine whether or not certain pieces (e.g.,50) or more of data among the data loaded in the reception buffers (1) through (100) are of high level. In this case, the step 390 clears all reception buffers (1) through (100). Although the step 520 of the first embodiment determines whether or not two or more framing errors have occurred continuously based on the state of the flag XFRERR, an alternative scheme is to provide a counter for counting the number of times of continuous occurrence of framing errors and inhibit the SIN interrupt process only when the count value become a certain number or more. In this case, the prescribed number of times of occurrence may be set to be the number of times of framing errors that occur at the starting of the vehicle so that the SIN interrupt is retained enabled despite the framing errors occurring at the starting of the vehicle, thereby allowing the inherent data communication based on the SIN interrupt. Although in the foregoing embodiments, the request message and response message are formed of multiple 1-byte data, these messages may be formed of multiple 2-byte data, or multiple 4-byte data, or even longer byte data. Although the foregoing embodiments are systems including the fault diagnostictester 5 as a master unit and electronic controllers as slave units, the present invention can be applied to systems in which arbitrary one of electronic controllers is a master unit and remaining electronic controllers are slave units. Although the foregoing embodiments are communication systems used for land vehicles, the present invention can be applied to control objects other than land vehicles. Although the foregoing embodiments are communication systems which perform data communication between a master unit and multiple slave units in 1-to-n relationship, the present invention can be applied to communication systems which perform data communication between a master unit and a slave unit in 1-to-1 relationship.

Claims: A communication system including a master unit (5) and slave units (1,2) connected through a communication line (3), said master unit (5) sending a request message that is formed of a plurality of certain byte data through said communication line (3) for requesting the execution of a certain process, said slave units (1,2) initiating an interrupt process upon detecting the stop bit of the byte data thereby to receive the byte data or sending a response message that is formed of a plurality of certain byte data over said communication line (3) upon receiving all of the byte data of the request message, wherein said slave units (1,2) include framing error detection means (515) for detecting a framing error which occurs when the stop bit of the byte data received in the interrupt process is not a correct value; and interrupt process inhibit means (525, 547) characterized in that said slave units furthermore include: frequent occurrence determination means (520,546, 549,552) which determines as to whether or not said framing error detection means (515) has detected framing errors at a high frequency; and that the interrupt process inhibit means (525,547) inhibits the interrupt process in response to the determination by said frequent occurrence determination means (520,546, 549,552) that said framing error detection means (515) has detected framing errors at a high frequency. A communication system according to claim 1, wherein said master unit (5) sends an initialization address, which is slower in communication speed than the transmission/reception speed of request message and response message and is formed of certain byte data, through said communication line (3). A communication system according to claim 2, wherein said slave units (1,2) further include: initialization address reception means (305) which receives bit data of the initialization address after said interrupt process inhibit means (525,547) has inhibited the interrupt process, said initialization address reception means (305) carrying out the reception process for all bit data of the initialization address. A communication system according to claim 3, wherein said initialization address reception means (305) samples 1-bit data of the initialization address at a certain timing and determines the 1-bit data to be of a high level or low level based on the sampled value. A communication system according to claim 3, wherein said initialization address reception means (305) includes: sampling means (355,360) which samples 1-bit data of the initialization address at a certain timing; number-of-sampling determination means (365) which determines as to whether or not the number of times of sampling has reached a certain count value; and 1-bit data determining means (375,380,385) which determines the 1-bit data to be a high level or low level based on the sampled value in response to the determination of said number-of-sampling determination means (step 365) that the number of times of sampling has reached the count value. A communication system according to any one of claims 3 through 5, further including: interrupt process enabling means (310) which enables the interrupt process on completion of the reception process for all bit data of the initialization address by said initialization address reception means (305). A communication system according to any one of claims 3 through 6, wherein said frequent occurrence determination means (520,546,549,552) comprises: means (520) for determining as to whether or not said framing error detection means (515) has detected framing errors a certain number of times or more continuously. A communication system according to any one of claims 1 through 6, wherein said frequent occurrence determination means (520,546,549,552) comprises: means (546,549) for determining as to whether or not the number of times of detection of framing errors by said framing error detection means (515) is a certain proportion or more with respect to the number of times of initiation of the interrupt process. A communication system according to any one of claims 1 through 6, wherein said frequent occurrence determination means (520,546,549,552) comprises: means (546,549) for determining as to whether or not the number of times of detection of framing errors by said framing error detection means (515) is a certain proportion or more with respect to the time period since the first detection of framing error by said framing error detection means (515). A communication system according to any one of claims 1 through 9, wherein said slave units (1,2) are installed on a land vehicle.

Inventors: OGURO HIROKAZU, TAKABA KATSUMI, OGURO, HIROKAZU, TAKABA, KATSUMI
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1996
Main classification: H04L1
IPC codes: H04L29, H04L12, H04Q9