JPH07245786A - Multiple communication equipment - Google Patents

Abstract

PURPOSE:To prevent a communication fault caused when a power supply voltage drops due to cranking or the like from being recognized to be a communication error by releasing a tentative error when a voltage of a common power supply drops to a prescribed voltage or below while the tentative error is recorded. CONSTITUTION:Tentative error release circuits CPU1, CPU2,... releasing a tentative error when it is detected that a voltage Vb of a common power supply BAT drops to 7 a prescribed voltage or below with a voltage drop detection circuit while communication fault detection circuits CPU1, CPU2,... record a tentative error/are provided to control units CTR1, CTR2,... respectively. When a communication fault takes place among the control units CTR1, CTR2,... it is recorded as a tentative error and when the communication fault does not disappear for a prescribed time, the tentative error is revised into a communication error. Furthermore, when it is detected that the voltage Vb of the common power supply BAT is decreased to be a prescribed voltage or below while communication fault detection circuits CPU1, CPU2,... record a tentative error, the tentative error is released.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex communication device for transmitting / receiving various kinds of information via multiplex transmission lines installed between a plurality of control units.

[0002]

2. Description of the Related Art There is known a multiplex communication apparatus for communicating between a master station control unit and a plurality of slave station control units arranged at various places of a vehicle through multiplex transmission lines (for example, Japanese Patent Laid-Open No. Hei 5). -236563 gazette). In this type of multiplex communication device, a master station control unit and a plurality of slave station control units are each provided with a microcomputer, and operation information of operating members connected to each slave station control unit is transmitted via a multiplex transmission line to the master station. It is transmitted to the station control unit, the master station control unit determines the drive of the corresponding terminal device based on the operation information, and the drive information is transmitted to the slave station control unit to which the terminal device is connected via the multiplex transmission line. is doing.

Communication between the master station control unit and the slave station control unit is performed in a predetermined order, and when there is no response from the slave station control unit at the communication destination, a communication error with the slave station is recorded and recorded. Communication errors are used as information for external failure diagnosis devices.

[0004]

The microcomputer has a so-called power-on / reset function, and is automatically reset when the power supply voltage supplied to the power supply terminal Vcc becomes equal to or lower than the reset level Vrs, and the power supply is reset again. When the voltage exceeds the reset level Vrs, the operation starts. The reset level Vrs varies from one microcomputer to another due to variations in elements. Therefore, even when power is supplied from the same power source to a plurality of control units, the reset timing may differ from each other by several msec.

Therefore, when the battery voltage drops when the vehicle is cranking or when the power source fails, there are microcomputers that are reset due to variations in the reset level Vrs and microcomputers that are not reset. In such a case, even if the control unit having the microcomputer that was not reset sent to the control unit having the microcomputer that was reset, it was not reset because there was no response from the control unit that was reset. The control unit will record communication errors with the reset control unit. Normally, a vehicle is cranked many times and is completed in a short time. Therefore, in such a case, it is desired to avoid recording a communication error even if a communication abnormality actually occurs.

However, in the conventional multiplex communication device,
Since it is not possible to distinguish between a communication error caused by a decrease in power supply voltage due to cranking, etc. and an original communication error caused by a failure in the communication circuit, microcomputer, control circuit, etc., even when the power supply voltage is decreased due to cranking, etc. There is a problem of recording communication errors.

It is an object of the present invention to provide a multiplex communication device in which a communication abnormality that occurs when the power supply voltage is lowered due to cranking or the like is not recognized as a communication error.

[0008]

When the present invention is described with reference to FIG. 1 showing an embodiment, the invention of claim 1 is automatically reset when the voltage of the common power source BAT drops to a specific value. Arithmetic control circuit CPU1, CPU2, CPU
A plurality of control units CTR each having 3, ...
, CTR2, CTR3, ..., Which are applied to a multiplex communication device which communicates with each other via a common multiplex transmission line LL. And a voltage drop detection circuit (R1, C1, D1, CPU1) for detecting that the voltage Vb of the common power supply BAT has dropped below a predetermined value higher than the specific value of each of the arithmetic control circuits CPU1, CPU2, CPU3 ,. When a communication error occurs in the communication between the control units, it is temporarily recorded as a temporary error, and when the communication error is not resolved for a predetermined time, the temporary error is switched to a communication error. Communication error detection circuits CPU1, CPU2, CPU3 ,.・
And the communication abnormality detection circuits CPU1, CPU2, CPU3,
When the voltage drop detection circuit detects that the voltage Vb of the common power supply BAT has dropped to a predetermined value or less while the provisional error is recorded by, the provisional error release circuits CPU1, CPU2, CPU3 that release the provisional error , ...
And control units CTR1, CTR2, CTR3 ,.
・ Prepare for and achieve the above objectives. Further, in the voltage drop detection circuit of the multiplex communication device according to claim 2, when the voltage Vb of the common power supply BAT rises, the output voltage Vc rises with a delay, and when the voltage Vb of the common power supply BAT drops, the output voltage Vc. Delay circuit (R1, C1,
D1), and when the output voltage Vc of the delay circuit is less than or equal to a preset value, it is determined that the voltage Vb of the common power supply BAT is less than or equal to a predetermined value. further,
According to the invention of claim 3, the microcomputers CPU1, CPU2, CPU3, ... Connected to the common power source BAT.
Control units CTR1 and CT each having
The present invention is applied to a multiplex communication device including R2, CTR3, ..., Which communicate with each other via a common multiplex transmission line LL. Then, when the voltage Vb of the common power source BAT rises, the output voltage Vc increases with a delay, and when the voltage Vb of the common power source BAT decreases, the output voltage Vc decreases almost at the same time (R1, C1, D1). , And the control units CRT1, CTR2, CTR3, ... By the microcomputers CPU1, CPU2, CPU3 ,.
When a communication error occurs during communication between the terminals, it is temporarily recorded as a temporary error, and when the output voltage Vc of the delay circuit (R1, C1, D1) becomes less than or equal to a preset value, the temporary error is canceled, thereby To achieve. The multiplex communication device according to claim 4 is a microcomputer CPU1, CP
The U2, the CPU 3, ... Switch the provisional error to the communication error if the communication error is not resolved and the provisional error remains recorded when a predetermined time has elapsed after recording the provisional error. .

[0009]

In the multiplex communication device according to the first aspect, when a communication error occurs in the communication between the control units, it is temporarily recorded as a temporary error, and when the communication error is not eliminated for a predetermined time, the temporary error is switched to the communication error. When it is detected that the voltage Vb of the common power supply has dropped to a predetermined value or less while the temporary error is recorded, the temporary error is canceled. The arithmetic control circuit automatically resets when the power supply voltage Vb drops to the reset level. This reset level is a unique value that differs for each operation control circuit, and there are operation control circuits that are reset due to variations in the reset level and operation control circuits that are not reset when the power supply voltage Vb decreases. In such a case, a communication abnormality occurs between the control unit having the arithmetic control circuit that has not been reset and the control unit having the arithmetic control circuit that has been reset. However, since it can be recognized that this communication abnormality has occurred due to the decrease in the power supply voltage Vb, it is possible to prevent such communication abnormality from being recognized as a communication error. Further, in the multiplex communication device according to claim 2, when the output voltage Vc of the delay circuit is equal to or less than the set value, the voltage V of the common power source
It is determined that b is less than or equal to a predetermined value. Common power supply voltage Vb
Is lower than the eigenvalue of the arithmetic control circuit, the arithmetic control circuit is reset. When the voltage Vb of the common power supply rises again and returns to a value higher than the predetermined value, the arithmetic control circuit starts the operation. At this time, the output voltage Vc of the delay circuit
Rises with a delay, the output voltage V of the delay circuit is delayed even in the arithmetic and control circuit that has been reset and then started its operation again.
If the value of c is less than or equal to the set value, it can be recognized that the voltage Vb of the common power supply has dropped to less than or equal to the predetermined value. Further, in the multiplex communication device according to claim 3, the voltage Vb of the common power supply BAT is input through the delay circuit, and when a communication error occurs in the communication between the control units, it is temporarily recorded as a temporary error and the output of the delay circuit. When the voltage Vc becomes equal to or lower than a preset value, the provisional error is released. The microcomputer automatically resets when the power supply voltage Vb drops to the reset level. This reset level is a unique value that differs for each microcomputer, and there are microcomputers that are reset due to variations in the reset level and microcomputers that are not reset when the power supply voltage Vb decreases. In such a case, a communication error occurs between the control unit having the microcomputer that has not been reset and the control unit having the microcomputer that has been reset. However, since it can be recognized that this communication abnormality has occurred due to the decrease in the power supply voltage Vb, it is possible to prevent such communication abnormality from being recognized as a communication error. In the multiplex communication device according to the fourth aspect, when a predetermined time has elapsed after the provisional error was recorded, if the communication error is not resolved and the provisional error remains recorded, the provisional error is switched to the communication error. This makes it possible to clearly distinguish between an original communication error caused by a failure of the communication circuit, the microcomputer, the control circuit, etc. and a communication error caused by the decrease of the power supply voltage, and it is appropriate only for the original communication error. Error handling can be performed.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the multiplex communication device of the present invention is applied to a vehicle to control various in-vehicle devices will be described. FIG. 1 is a functional block diagram showing the configuration of the embodiment. A master station control unit (hereinafter, simply referred to as a master station) CTR1 arranged near the driver's seat of the vehicle includes a plurality of slave station control units (hereinafter, referred to as a master station) arranged at various places of the vehicle through the multiplex transmission line LL. CTR2, CTR3, ..., which are simply called slave stations, are connected. The master station CTR1 includes a microcomputer (hereinafter referred to as CPU) 1 and an interface circuit IF.
1, a ROM that stores a communication control program, a battery backup RAM that records a temporary error and a communication error during communication, and a power supply circuit PS1. CPU
1 communicates with the slave stations CTR2, CTR3, ... Via their respective interface circuits IF1, IF2, IF3, ..., And drives corresponding terminal devices based on the operation information of the operating members received from the slave stations. Then, the drive information is transmitted to the slave station to which the terminal device is connected.

Power is supplied to the power supply terminal Vcc of the CPU1 from the battery BAT via the terminal TB1 and the power supply circuit PS1. Normally, the terminal voltage of the in-vehicle battery BAT is 1.
Since it is 2V, the battery voltage Vb is stepped down to a predetermined voltage by the power supply circuit PS1 and supplied to the CPU1. Further, the COM terminal of the CPU1 is connected to the ground line of the battery BAT via the terminal TB2. Furthermore, the master station CT
A delay circuit in which a resistor R1 and a capacitor C1 are connected in series is connected between terminals TB1 and TB2 of R1, and a diode D1 is connected in parallel to the resistor R1 in the direction shown in the drawing, and further connected to the resistor R1. The connection point of the condenser C1 is connected to the AD terminal of the CPU1. This AD terminal is C
It is an input terminal of the AD converter built in PU1.

FIG. 2 and FIG. 3 are views showing the changes over time in the battery voltage Vb and the capacitor terminal voltage Vc during cranking of the vehicle, and FIG. 2 shows the battery voltage Vb being C
FIG. 3 shows the time when the voltage drops below the reset level Vrs of the PU, and FIG. 3 shows the time when the battery voltage Vb drops below the predetermined level Vo (here Vo> Vrs) which is higher than the reset level Vrs. When the vehicle is cranking, a large amount of electric power is supplied from the battery BAT to the starter, so that the terminal voltage Vb drops. When the engine starts and the power supply to the starter is stopped, the battery terminal voltage V
b is almost restored to the original voltage level. Since the capacitor C1 is charged by being supplied with electric power from the battery BAT via the resistor R1, the capacitor terminal voltage Vc is substantially equal to the battery voltage Vb in a steady state. When the battery terminal voltage Vb drops during cranking, the capacitor C1 is discharged through the diode D1 and the capacitor terminal voltage Vc drops almost in the same manner as the battery voltage Vb. The battery voltage Vb sharply decreases at the start of cranking, but thereafter gradually increases while vibrating to some extent. At this time, the charging of the capacitor C1 is started again with the rise of the battery voltage Vb, and the capacitor terminal voltage Vc is changed according to the time constant determined by the capacitance of the capacitor C1 and the resistance value of the resistor R1 as shown by the broken line in the figure. To rise. When the cranking is stopped at time t2 in FIG. 2, the battery voltage Vb rapidly recovers to almost the original level, but the capacitor C1
Is charged via the resistor R1, its terminal voltage Vc
Rises along the broken line according to the above time constant.

The CPU restarts its operation at time t2 when the battery voltage Vb recovers to the original level when it exceeds the predetermined voltage Vo. Therefore, by the CPU that has restarted the operation, the capacitor terminal voltage Vc and the predetermined voltage Vc are exceeded by the time t3 when the capacitor terminal voltage Vc exceeds the predetermined voltage Vo.
Compared with o, the capacitor terminal voltage Vc is the predetermined voltage V
If it is lower than o, it can be recognized that the CPU has been reset due to the decrease in the battery voltage Vb accompanying the cranking.

Even if the battery terminal voltage Vb does not drop to the reset level Vrs, the capacitor terminal voltage Vc drops sharply at the same time as the battery voltage Vb at the cranking start time t5, as shown in FIG. At the cranking end time t6, the battery voltage Vb rapidly recovers to almost the original level, but the capacitor terminal voltage Vc
Rises along the broken line according to the above time constant. In this case, since the CPU has not been reset, the time t5
To the time t7 at which the capacitor terminal voltage Vc exceeds the predetermined voltage Vo, the capacitor terminal voltage Vc and the predetermined voltage Vo are compared, and if the capacitor terminal voltage Vc is lower than the predetermined voltage Vo, the battery voltage is accompanied by cranking. It can be recognized that Vb has decreased.

When there is no response from the communication destination slave station, the CPU 1 temporarily makes a temporary communication error with the slave station (hereinafter,
(Temporary error) is recorded in the RAM of the battery back amplifier. After that, if there is no response from the slave station even after a lapse of a predetermined time, the provisional error is changed to a communication error and a predetermined error process is performed. When it is detected that the capacitor terminal voltage Vc is lower than the predetermined voltage Vo when the provisional error is recorded, the CPU 1 determines that the provisional error with the slave station has occurred due to the decrease in the battery voltage Vb due to the cranking. , Release the provisional error recorded in the RAM.

The slave station control unit CTR2 is installed near the driver's seat of the vehicle, and has a CPU 2 and an interface circuit IF.
The same equipment as the parent station CTR1 such as 2 is provided. Although illustration is omitted, this slave station CTR2 is the master station CTR.
It is equipped with a power supply circuit similar to that of 1, and the battery BA
Electric power is supplied from T to the CPU 2. This child station CTR2
A small lamp switch for turning on / off a meter lighting lamp, a headlamp switch for turning on / off a headlamp, and a turn signal switch for turning on / off a turn signal lamp are connected to the. The slave station control unit CTR3 is installed near the driver's seat of the vehicle, and includes the same devices as the master station CTR1 such as the CPU 3 and the interface circuit IF3. Although not shown, this slave station CTR3 is equipped with a power supply circuit similar to that of the master station CTR1.
Power is supplied to U3. The slave station CTR3 is connected with a switch for opening / closing the window of the passenger seat, a switch for opening / closing the windows on the left and right of the rear seat, a switch for door lock, and the like. In addition to the above slave stations, various slave station control units are connected to the master station CTR1 via the multiplex transmission line LL in the vehicle, but the description of these slave stations will be omitted.

4 and 5 show the CPU of the master station CTR1.
3 is a flowchart showing a control program executed in 1. The operation of the embodiment will be described with reference to these flowcharts. When power is supplied from the battery to the master station control unit CTR1 and a predetermined voltage is supplied to the terminal Vcc of the CPU1, the CPU1 executes a predetermined reset sequence and then starts execution of the communication control program shown in FIG. . In step S1, after transmitting drive information and the like to the slave station CTR2, the process proceeds to step S2 and the slave station CTR2.
Wait for a response from. If there is a response from the slave station CTR2, the process proceeds to step S8, and if not, the process proceeds to step S3. In step S8, the driving of the corresponding terminal device is determined based on the operation information of the switches sent from the child station CTR2, and the process proceeds to step S9 to send the driving information to the child station CTR3.

When there is no response from the slave station CTR2 in step S2, battery backup RA is performed in step S3.
The provisional error is recorded in M, the process proceeds to step S4, and the CPU
Start the timer built into 1. In a succeeding step S5, it is determined by a timer interrupt routine which will be described later whether or not the provisional error is released, and if released, the process returns to the step S1 and again transmits to the slave station CTR1.
If the provisional error has not been canceled, the process proceeds to step S6. In step S6, it is determined whether or not the set time T1 of the timer has elapsed, and when the time T1 has elapsed, step S7
Otherwise, return to step S1. After the provisional error is recorded, when the set time T1 has passed without being canceled by the timer interrupt routine, the provisional error is changed to a communication error in step S7, a predetermined communication error process is performed, and the process proceeds to step S9. . Note that the communication processing for the slave station CTR3, ... After step S9 is similar to the above-described processing for the slave station CTR2.
The description is omitted.

The CPU 1 has a predetermined time, for example, 10 mse.
A timer interrupt occurs every c, and the CPU 1 executes the timer interrupt routine shown in FIG. Step S
At 21, it is determined whether the capacitor terminal voltage Vc is lower than the predetermined voltage Vo. If Vc <Vo, step S
Proceed to 22, otherwise return. Step S
At 22, it is determined whether or not a provisional error is recorded in the battery backup RAM, and if it is recorded, the process proceeds to step S23, and if not, the process returns. If it is detected that the capacitor terminal voltage Vc is lower than the predetermined voltage Vo while the temporary error is recorded, it is determined that the temporary error with the slave station has occurred due to the decrease in the battery voltage Vb due to cranking, and the step RA in S23
Cancel the provisional error recorded in M and return.

Now, during communication between the master station CTR1 and the slave station CTR2, the battery voltage Vb drops due to cranking or the like, and the slave station CTR2 has a variation in the reset level Vrs of the CPU1 and the CPU2 as shown in FIG. If the master station CTR1 is reset and is not reset as shown in FIG. 3, the slave station CTR2 cannot respond to the transmission from the master station CTR1. Therefore, the master station CTR1 and the slave station C are not able to respond.
Communication with TR2 is disabled. The master station CTR1 temporarily records the temporary error for the slave station CTR2, but thereafter, when the timer interrupt routine is executed and it is detected that the capacitor voltage Vc is lower than the predetermined voltage Vo, the communication failure is caused by the battery due to cranking. The CPU 2 of the slave station CTR2 recognizes that the error has occurred because the CPU 2 of the slave station CTR2 has been reset with the decrease in the voltage Vb, and cancels the provisional error.

On the other hand, during communication between the master station CTR1 and the slave station CTR2, the battery voltage Vb drops due to cranking or the like, and the reset levels Vrs of the CPU1 and CPU2 are generated.
Assuming that the master station CTR1 is reset as shown in FIG. 2 and the slave station CTR2 is not reset as shown in FIG. 3 due to the variation of, the CPU1 of the master station CTR1 that resumes operation after the end of cranking starts from time t2. Before the time t3, the timer interrupt routine recognizes that the capacitor voltage Vc is lower than the predetermined voltage Vo, and as the battery voltage Vb decreases due to cranking or the like, the CPU 1 resets itself and the slave station CTR2. Recognize that communication has been interrupted.

In the above-described embodiments, the multiplex communication device of the present invention is applied to a vehicle to control various in-vehicle devices, but the present invention can be applied to other than the vehicle. Further, in the above-described embodiment, an example of communicating with each slave station around the master station is shown, but the present invention is also applicable when each control unit executes the above-mentioned control program to communicate with another control unit. Can be applied. Furthermore, in the above-described embodiment, the description has been centered on the decrease in battery voltage due to cranking,
The multiplex communication apparatus of the present invention is not limited to the cranking operation, and operates in the same manner as the cranking even when the power supply voltage is lowered due to a failure of the power supply circuit or the like.

In the configuration of the above embodiment, the microcomputers CPU1, CPU2, CPU3, ... Are provided with an arithmetic control circuit, a voltage drop detection circuit, a communication abnormality detection circuit and a temporary error cancellation circuit, a resistor R1 and a capacitor C.
1 and the diode D1 respectively form a delay circuit.

[0025]

According to the first aspect of the present invention, when a communication error occurs in communication between control units, it is temporarily recorded as a temporary error, and when the communication error is not resolved for a predetermined time, the temporary error is switched to a communication error. The provisional error is canceled when it is detected that the voltage of the common power supply has dropped below a predetermined value while the provisional error is recorded. The arithmetic and control circuit automatically resets when the power supply voltage drops to the reset level. This reset level is a unique value that differs for each arithmetic control circuit.There are arithmetic control circuits that are reset due to variations in the reset level of the arithmetic control circuits when the power supply voltage drops, and arithmetic control circuits that are not reset. A communication error occurs between the control unit having the arithmetic control circuit that did not exist and the control unit having the reset arithmetic control circuit. However, since it is possible to recognize that this communication abnormality has occurred due to the drop in the power supply voltage, it is possible to prevent such communication abnormality from being recognized as a communication error, and also to use communication circuits, microcomputers, control circuits, etc. The distinction between the original communication error caused by the failure and the communication error caused by the decrease of the power supply voltage is made clear, and the appropriate error processing can be performed only for the original communication error. Furthermore, when controlling various in-vehicle devices by applying it to a vehicle, since the cranking operation of the vehicle can be recognized, communication between control units is started before cranking, and communication accompanying the cranking operation is performed on the way. Even if an abnormality occurs, the communication error can be prevented from being recognized, and various new functions can be added to the vehicle. For example, in order to prevent malfunctions due to communication abnormalities during cranking, the anti-theft function of the vehicle that was activated after cranking should also be activated before cranking, and the engine itself should be started when theft is detected. It is possible to prohibit it. Further, according to the invention of claim 2, when the output voltage of the delay circuit is equal to or less than the set value, it is determined that the voltage of the common power source is equal to or less than the predetermined value. When the voltage of the common power supply drops below the specific value of the arithmetic control circuit, the arithmetic control circuit is reset. When the voltage of the common power supply rises again and returns to a value higher than the predetermined value, the arithmetic and control circuit starts operating. At this time, the output voltage of the delay circuit rises with a delay.Therefore, even if the operation control circuit that resets and then starts operation again, if the output voltage of the delay circuit is less than or equal to the set value, the common power supply voltage is less than or equal to the specified value. It can be recognized that it had fallen to. Further, according to the invention of claim 3, the voltage of the common power source is input through the delay circuit, and when a communication error occurs in the communication between the control units, it is temporarily recorded as a temporary error, and the output voltage of the delay circuit is The provisional error is canceled when the value becomes equal to or less than the preset value. The microcomputer automatically resets when the power supply voltage drops to the reset level. This reset level is a unique value that differs for each microcomputer, and there are microcomputers that are reset due to variations in the reset level and microcomputers that are not reset when the power supply voltage drops. In such a case, a communication error occurs between the control unit having the microcomputer that has not been reset and the control unit having the microcomputer that has been reset. However, since it is possible to recognize that this communication abnormality has occurred due to the decrease in the power supply voltage, it is possible to prevent such communication abnormality from being recognized as a communication error. According to the invention of claim 4, when the predetermined time elapses after the provisional error is recorded, if the communication error is not resolved and the provisional error remains recorded, the provisional error is switched to the communication error. The distinction between the original communication error caused by the failure of the communication circuit, the microcomputer, the control circuit, etc. and the communication error caused by the decrease of the power supply voltage is clarified, and the appropriate error processing is performed only for the original communication error. It can be carried out.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of an embodiment.

FIG. 2 is a diagram showing a time change of a battery voltage Vb and a capacitor terminal voltage Vc during cranking.

FIG. 3 is a diagram showing a time change of a battery voltage Vb and a capacitor terminal voltage Vc during cranking.

FIG. 4 is a flowchart showing a communication control program.

FIG. 5 is a flowchart showing a timer interrupt routine.

[Explanation of symbols]

CTR1 Master station control unit CTR2, CTR3 Slave station control unit CPU1, CPU2, CPU3 Microcomputer IF1, IF2, IF3 Interface circuit PS1 Power supply circuit C1 Capacitor R1 Resistor D1 Diode BAT Battery LL Multiple transmission line

Claims (4)

[Claims] 1. A plurality of control units each having an arithmetic and control circuit that automatically resets when the voltage of a common power source drops to a specific value, and these control units communicate with each other via a common multiplex transmission line. In a multiplex communication device, a voltage drop detection circuit that detects that the voltage of the common power supply has dropped below a predetermined value higher than the eigenvalue of each arithmetic control circuit, and when a communication error occurs in communication between the control units. Is temporarily recorded as a provisional error, and then, when the communication error is not eliminated for a predetermined time, a communication abnormality detection circuit that switches the provisional error to a communication error, and when the provisional error is recorded by the communication abnormality detection circuit, When the voltage drop detection circuit detects that the voltage of the common power supply drops below the predetermined value, the provisional error is released. A multiplex communication device, characterized in that each control unit is provided with an error canceling circuit. 2. The multiplex communication device according to claim 1, wherein when the voltage of the common power supply rises, the output voltage delays and rises when the voltage of the common power supply rises, and when the voltage of the common power supply falls. Has a delay circuit in which the output voltage decreases almost at the same time, and when the output voltage of the delay circuit is less than or equal to a preset value, it is determined that the voltage of the common power source is less than or equal to the predetermined value. Multiplexer. 3. A plurality of control units each having a microcomputer connected to a common power source,
In a multiplex communication device in which they communicate with each other via a common multiplex transmission line, when the voltage of the common power supply rises, the output voltage rises with a delay, and when the voltage of the common power supply drops, the output voltage increases. Is provided at the same time, the microcomputer reduces the output voltage of the delay circuit to a preset value or less when the communication error occurs in the communication between the control units. In this case, the multiplex communication device is characterized in that the temporary error is released. 4. The multiplex communication apparatus according to claim 3, wherein the microcomputer does not eliminate the communication abnormality and records the temporary error when a predetermined time has elapsed after recording the temporary error. If so, the multiplex communication device is characterized in that the temporary error is switched to a communication error.