JPH048018A - Multiplex communication system - Google Patents

Abstract

PURPOSE:To continue the communication even when a fault decreasing a signal level of a transmission message takes place by replacing a reference signal level into a 2nd reference signal level lower than that of the 1st reference signal level when a comparison signal is not normally detected within a prescribed time. CONSTITUTION:When power supply to a transmission station 1(100) is stopped while the multiplex communication system is in operation, a communication bus 400 is connected to ground with a low impedance. Thus, since a signal level of a transmission message is deteriorated and does not exceed a threshold level, an output of a comparator 308 is unchanged. When no change is caused in the output of the comparator 308 even lapse of a prescribed time, a monitor 309 outputs a switching signal to switching elements 306, 307 to replace the threshold level into a 2nd reference signal level V2(312). When the 2nd reference signal level V2(312) is set lower than Vdd/2, the output of the comparator 308 is changed and the communication is continued.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multiplex communication system in which transmission data is transmitted and received via a common communication bus, such as one or more receiving stations and a plurality of transmitting stations.

[Prior art]

An example of a conventional multiplex communication system is one shown in FIG. 4, for example. FIG. 4 shows a transmitting station 1 consisting of a transmitting device 101 for controlling data transmission, a limiting resistor 102 for surge protection, and diodes 103 and 104.
(100), a transmitting station 2 (200) having the same configuration as transmitting station 1 (100), a resistor 301, and a capacitor 302.
A filter circuit consisting of a reference signal generator consisting of a ladder resistor 313 and 314, and a diode 32 for surge protection.
1, a receiving station 300 consisting of a comparator 308, a monitoring device 309, and a receiving device 310, and a communication bus 40.
0, and a power supply Vdd that supplies power to transmitting station 1 (100), transmitting station 2 (200), and receiving station 300, respectively.
1 (411), Vdd 2 (421'l,
Vdd 3 (431).

Each power supply Vdd 1 (411), Vdd 2 (421
), Vdd 3 (431)k protective fuses 410, 420, 430 and transmitting station 1 (100
) and a load 401 connected to the same power line.

Figure 4? The operation of this multiplex communication system will be explained using the following.

■ Communication operation For example, when information to be transmitted occurs at transmitting station 2 (200'), transmitting station 2 (200)
Transmission message in 1? A transmission message is generated and outputted to the communication bus 400 via the limiting resistor 102 at a predetermined timing. The receiving station 300 receives the next transmitted message output from the transmitting station 2 (200) via the gold communication bus 400. At the receiving station 300, the noise contained in the transmitted message is first removed by a filter circuit, and the ladder resistors 313, 3
14 ↓Reference signal level V 3 (315'l) is obtained by comparing the signal level of the transmitted message that has completely passed through the filter circuit with the comparator 308, and the next comparison signal is received as received data and is received by the monitoring device 309. After checking the data, the receiving device 310 performs processing such as decoding the received data.

■ Surge protection Communication bus 400? When a surge is applied through.

Each transmitting station releases the surge current to the flLk power supply side through the limiting resistor 102 and the diode 103 in the case of a positive surge, and releases the surge current through the limiting resistor 102 and the diode 104 in the case of a negative surge. By letting the current escape to the ground side, the input end of the transmitting device 101 is prevented from being destroyed. Further, in the receiving station 300, similarly to the transmitting station, diodes 321 and 322 prevent the ten terminals of the comparator 308 from being destroyed.

■ Is the safety of transmission WIAv control communication? To ensure this, the following methods are being taken. Is there a margin for fluctuations in the signal level of the transmitted message due to ground fluctuations or surge application on the communication bus 400? In order to ensure this, the low value [reference signal level v3 (315)] is set larger than Vdd/2 and the waveform is shaped by the comparator 308. A monitoring device 309 monitors the reception status of received data in order to check whether communication is disabled due to a communication failure. Furthermore, in order to prevent transmission errors due to communication failures, parity and CRC (CRC) are added to the data transmitted by the transmitting device 101 of the transmitting station.
yclic Redundancy Cheek')
f is added to generate a transmission message, and the monitoring device 309 of the receiving station performs parity-CRC' (i-check).
“Basics and practice of microcomputer data transmission”,
Written by Makoto Miyazaki.

CQ Publishing, pp. 87-107] [Problem that 8A attempts to solve] However, in the conventional multiplex communication 7 system system described above, the power supply paths to each transmitting station and receiving station are often different. As a result, the following problems frequently occurred.

The multiplex communication system shown in FIG. 4 is configured, for example, in a vehicle using a power source Vdd 1 (411).

Vdd 2 (421), Vdd 3 (431)'
t"-t Resole 7 Ri-1 = + ri system power supply, ignition system power supply, buff + !J - system power supply 1. Transmitting station 1
(100)' to rear armrest SW9 transmitting station 2 (
200) is a cluster SW, a receiving station 300t control unit, and a negative W401t-air conditioner blower motor.

Here, if the power supply to the rear armrest SW [transmission station 1 (100)] stops while the multiplex communication system is in operation, for example due to the fuse 410 of the accessory system power supply blowing out, the first communication bus 400 From rear armrest SW limiting resistance 102. Dio-1'103.1tt source line, floor motor for air conditioner [load 401)' ((
Since a current path is formed through the communication bus 400 to the ground side, the communication bus 400 is in a grounded state with low impedance.

Therefore, even if an attempt is made to operate the cluster SW [transmitting station 2 (200)] that is powered from the ignition system power source, the signal level of the transmitted message on the communication bus 400 drops as shown in FIG. Control unit [receiving station 30] that is supplied with power from the power supply
0], the high potential signal level (-I level) of the transmission data does not exceed the threshold value [reference signal level V 3 (315)], so the output of the comparator 308 does not change and normal reception cannot be performed, making it impossible to operate. becomes.

Therefore, even if the power supply to one line stops, communication between the transmitting and receiving stations that are supplied with power becomes impossible, and all functions of units controlled by the multiplex communication system stop. I'm sorry for the problem.

Furthermore, even if a failure occurs in the communication bus 400 itself (for example, if the connector part of the transmission line is short-circuited to the vehicle body due to a foreign object, Wi, @, etc.), the communication bus 400 is grounded with low impedance and the same communication failure occurs. The problem of causing it is rare.

[Next method to solve the problem]

This invention was made in view of the following problems mentioned above.
If the receiving station cannot normally detect the comparison signal within a predetermined time, it outputs the full switching signal, and uses the switching signal to switch to the second reference signal level, which is lower than the reference signal level. The purpose is to resolve the issue.

[Effect]

If the transmission message cannot be detected normally within a predetermined time by monitoring the comparison signal at the receiving station 1. For example, if the communication bus is grounded with low impedance due to power supply to one system being stopped, the communication bus The signal level of the above transmitted message drops and the high potential signal level of the transmitted message no longer exceeds the reference signal level, so the receiving station cannot confirm a change in the comparison signal, and nothing happens even after a predetermined period of time has elapsed. Even if it is determined that reception is not possible, it is possible to continue communication by switching the reference signal level to the second reference signal level, which is a lower signal level, without immediately determining that communication is impossible. Does this mean that the entire function controlled by the system stops? It can be prevented.

〔Example〕

Hereinafter, description will be given based on specific examples.

FIG. 1 shows an embodiment of this invention. FIG. 1 shows a multiplex communication system configured within a vehicle, for example. In FIG. 1, 100 is the transmitting station 1;
00) is composed of a transmitter 101, a limiting resistor 102, and diodes 103 and 104. A transmitting device 101 that controls data transmission has a limiting resistor 1 for surge protection.
A diode 103 for surge protection is connected to the communication bus 400 through the power supply line, an anode is connected to the output terminal of the transmitting device 101, a diode 104 is connected to the output terminal of the transmitting device 101, and a diode 104 for surge protection is connected to the communication bus 400 through the ti cathode.
The rare node connected to the output end of the node is all connected to the ground side. Transmitting station 2 (200) has the same configuration as transmitting station 1 (100).

In the receiving station 300, a communication bus 400 and a terminal of a comparator 308 are connected via a filter circuit including a resistor 301 and a capacitor 302, and a switching element 306
, 307 through ladder resistors 303, 304.

305 reference signal generator c reference signal level V
1 (311), V 2 (312) k are generated. However, V 1 (311)) V 2 (312'
)) is connected to one terminal of the comparator 308, and the output terminal of the comparator 308 is connected to the monitoring device 309, which is the monitoring device i1309.

The switching elements 306 and 307 output the received data to the receiving device 310 and also output switching signals for switching the reference signal levels V 1 (311) and V 2 (312).
It is configured to output to. In addition, a surge protection diode 321 of the receiving station 300 has a cand connected to the power supply line and connected to the ten terminal of the anode i comparator 308, and a diode 104 for surge protection connected to the ten terminal of the comparator 308 to the fi cathode. Connected to the ground side. Transmitting station 1 (100).

The transmitting station 2 (200) and the receiving station 300 have power supplies Vdd 1 (411), Vdd 2 (420,
Power is supplied from Vdd 3 (431), and each power supply V
dd 1 (411), Vdd 2 (421),
Vdd 3 (431') is fuse 410, 420
.

430, and a load 401 is connected to the same power line as transmitting station 1 (100). FIG. 3 shows the transmission status of the transmission messages sent by the transmitting stations 100, 2 [10]. Each transmitting station Zoo, 200, sends a transmitted message with message time T1 to interval time T.
They are sent out in order at intervals of 2.

Figure 1? The operation of this multiplex communication system will be explained using the following.

■ Communication operation For example, when the transmitting station 2 (200) sends out all transmission messages, the transmitting station 2 (200) generates a transmission message based on the information i to be transmitted by the transmitting device 101, and at a predetermined timing, transmits the limiting resistor 102. The transmission message is output to the communication bus 400 via the communication bus 400. The receiving station 300 is the transmitting station 2
Transmission message outputted by (200') 7 communication bus (4
00) t-receive via. At the receiving station 300, the reference signal level V 1 is normally set by the switching switch 306.
(311') is selected C. First, noise contained in the transmitted message is removed by a filter circuit.

Comparator 3 compares the signal level of the transmission message passed through the filter circuit with the base S signal level V 1 (312).
08, the data is compared, waveform shaped, and received as received data. After the monitoring device 309 changes all of the received data, the receiving device 310 performs processing such as decoding the received data + uIHL.

■ Surge protection Communication bus 400? When a surge is applied through.

Transmitting station 1 (100) and transmitting station 2 (200) release the surge current to the power supply side through the limiting resistor 102 and diode 103 in the case of a positive surge, and release the surge current to the power supply side through the limiting resistor 102 and the diode 103 in the case of a negative surge. Is it possible to destroy the input terminal of the transmitting device 101 by letting the surge current escape to the ground side via the diode 104? Preventing. In addition, the receiving station 30
0 is connected to diodes 321 and 32 similarly to the transmitting station.
2 destroys the comparator 308 O+ terminal? Preventing.

■ To ensure the safety of transmission AV control communications, the following methods are used. In order to maintain a margin kW against fluctuations in the signal level of the transmitted message due to ground fluctuations or surge application on the communication bus 400, a commonly used threshold value [base signal level v1 (311)''l t-Vdd /
The waveform is shaped by the comparator 308 with a setting larger than 2p. A monitoring device 309 monitors the reception status of received data in order to completely monitor whether communication is disabled due to a communication failure.

Furthermore, in order to prevent transmission errors due to communication failure, parity and C
RC'! il-added to the transmitter, and the receiving station's monitoring device 309 generates a parity/CRC? rCheck 0 ■ Operation when power supply is stopped If the power supply to transmitting station 1 (100) is stopped while the multiplex communication system is in operation, for example due to fuse 410 blowing out, 1. Transmitting station 1 (
110) limiting resistance 102. Diode 103. Since a current path is formed to the ground side via the power supply line and the load 401, one communication path 400 is in a grounded state with low impedance. Due to this hole, the signal level of the transmitted message on the communication bus 400 drops, as shown in FIG.
Since the high potential signal level of the transmission message exceeds the threshold (reference signal level Vl (311)) t-, the output of the comparator 308 does not change. The monitoring device 309 monitors the output t of the comparator 308 for a predetermined time [for example, message time T1+ as shown in FIG.
Interval time T2] There is no change in the output of the comparator 308 even if the full power is exceeded.In other words, it is determined that the transmission message cannot be received, and the switching element 306
307 and set the threshold below the second reference signal level V 2 (312) k Vdd / 2, the high potential signal level of the transmitted message will be equal to the threshold [second Reference signal level V 2 (312) 1
Nine times beyond k, the output of the comparator 308 changes, and the monitoring device 309 receives the transmission message? You will be able to confirm this and continue communication.

Furthermore, if a failure occurs in one communication path 400 itself (for example, a failure such as a short circuit to the vehicle body due to a foreign object in the connector part of the transmission path) and the communication bus 400 is grounded with low impedance, a similar communication failure problem will occur. , it is possible to take measures in the same manner as above.

He's a friend, and communication in this state is only temporary.
The signal level of the transmitted message is lower than 2>EW, making it vulnerable to disturbances such as noise. For this reason, the receiving station 300 has a function of notifying the user that the current communication state is temporary, by means of an alarm or the like.

Further, the threshold gold second reference signal level V 2 (312
), the high potential signal level of the transmitted message remains at the threshold (@22 reference signal level V 2 (312))
If the monitoring device 309 cannot confirm the reception of the received data and cannot fully recover the communication, it stops the function of the multiplex communication system.

The above description has been made based on the embodiment shown in FIG. 1, but the threshold value may be switched in multiple stages so that the threshold value can be gradually lowered.

〔Effect of the invention〕

The above has been explained based on specific examples.
If the receiving station cannot normally detect the comparison signal within a predetermined time, the receiving station outputs the full switching signal, and uses the switching signal to switch to a second reference signal level that is lower than the reference signal level, thereby supplying power to one system, for example. stops, the impedance of the communication bus is low, the signal level of the transmitted message on the communication bus drops, and at the receiving station, the high potential signal level of the transmitted message no longer exceeds the reference signal level, and there is no change in the comparison signal for more than a predetermined time. I haven't received anything since
Even if it is determined that communication is not possible, the receiving station does not immediately determine that communication is impossible, but instead switches the reference signal and continues communication? can be achieved. therefore.

Communication bus〃S is grounded with low impedance, making it possible to continue communication even in the event of a failure that reduces the signal level of transmitted messages on the communication bus, and all functions controlled by a multi-channel system. can be prevented from stopping, and the above-mentioned problem can be solved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing the signal levels of messages transmitted on the communication bus of the present invention, and FIG. FIG. 4 is a block diagram showing a conventional multiplex communication system; FIG. 5 is a diagram showing the signal level of transmission data on a conventional communication bus. 100 200: Transmitting station, 101 : transmitting device, 102
:103, 104, 321, 322: Surge protection, 400: Communication bus, 300: Receiving station, resistor for router, 302: Container for filter, 307
: Sinching element, 303. , 313, 314: Ladder resistance, 308: Ko30
9: Monitoring device, 310: Processing device, 410, 420
, 430: Fuse, 411°: Power supply limiting resistor. Diode 301: Fincer, 306 304, 305 Load on inverter 40, 421, 431 2nd f! 1 Patent Applicant Nissan Motor Co., Ltd.

Claims (1)

[Scope of Claims] The transmitting station includes one or more receiving stations, multiple transmitting stations, and a communication bus, and the transmitting station generates a transmission message having a predetermined format including data to be transmitted, and Sending a transmission message to the communication bus at predetermined time intervals, the receiving station generates a reference signal level that is a reference for receiving the transmission message, and inputs the reference signal level and the communication bus via the communication bus. In the multiplex communication system, the receiving station compares the signal level of the transmitted message with the signal level of the transmitted message and reads the data based on the comparison signal obtained by the comparison, A multiplex communication system characterized by outputting a switching signal when the signal level is not possible, and switching to a second reference signal level lower than the reference signal level by the switching signal.