JPS61187056A - Abnormality monitor circuit of transmission unit for multidrop serial bus - Google Patents

Abstract

PURPOSE:To prevent troubles of a local station from having influences upon the whole of a system by disconnecting a transmission driver from a multidrop serial bus when a reception data signal is held in the active level over a certain time. CONSTITUTION:When a reception data signal SD is held in the low level (the active level of a bus 10) over a certain time, a retriggerable monostable multivibrator E6 detects abnormality to reset a flip flop E7, and a relay 12 is turned off the disconnect the transmission driver from the bus 10. If the cause of abnormality exists in the local station, the signal SD is in the low level as it is though the relay 12 is turned off, and consequently, the relay 12 is turned off as it is. If the cause of abnormality exists in another station, the signal of the local station is switched to the high level when the relay 12 is turned off, and the flip flop E7 is set by the action of monostable multivibrators E4 and E5, and the relay 12 is turned on again. If the bus 10 is switched to the high level during this operation, the operation is restarted.

Description

Detailed Description of the Invention A% Industrial Application Field This invention relates to a transmission unit that uses a multi-drop serial bus as a transmission line, and in particular, to prevent an abnormality in the transmission system from spreading to the bus. Regarding monitoring circuits.

B1 Summary of the Invention This invention provides a transmission unit that connects a transmission driver to a multidrop serial bus by wired logic, and includes a switch means for disconnecting the connection point between the output end of the transmission driver and the input end of the receiver from the bus. When the received data signal obtained by the restorer remains at an active level for a certain period of time or more, the switch means is turned off, and if the received data signal returns to an inactive level by turning off, it is determined that there is no abnormality in the local station and the switch is turned off. By configuring the circuit so that if the switch is turned on and the received data signal remains at an active level, it is determined that there is an abnormality in the own station and the switch means is kept off, the bus will remain active even if the transmitting system of the own station fails. This makes it possible to avoid a system down state in which the entire system is fixed in an active state.

C5 Conventional Technology In a general transmission system using a multi-drop serial bus, each transmission driver of a large number of transmission units is connected to the bus by wired logic, and in each transmission system, the transmission data input of the transmission driver is set to a fixed level when not transmitting. The configuration is such that the transmission data is input to the transmission driver by a binary change of an active level and an immobile level at the time of transmission.

In this transmission system, when a certain transmission unit outputs an active level signal (in the case of an open collector type transmission driver, it outputs an L level signal), the entire serial bus becomes active level.

Therefore, if a failure occurs in the transmission system of a transmission unit and that transmission unit continues to output an active level signal, the bus will also be fixed at the active level, which will affect not only the transmission unit where the failure occurred but also the entire system. The effect of the failure spreads to the other units, making it impossible to transmit data between any units. In other words, the system will go down.

In order to avoid this system down, conventionally, each transmission unit has a CP that controls transmission control and data processing.
The U (Central Processing Unit) executes an abnormality diagnostic program to detect failures that cause the bus to be fixed at the active level.
If the failure occurs in its own transmission unit, control is performed to disconnect the transmission system of that unit from the bus. In this way, transmission using the bus becomes possible between healthy units.

D0 Problems to be Solved by the Invention The above-mentioned advanced abnormality diagnosis using a CPU can be performed relatively easily in a so-called intelligent terminal equipped with a CPU. However, in recent years, this type of multi-drop serial bus type transmission system has been widely applied to a variety of devices, and examples are also being seen in which a simple sensor, actuator drive circuit, etc. constitute one transmission unit. It has become. This type of simple functional unit does not include a sophisticated CPU and therefore cannot perform bus abnormality diagnosis as seen in intelligent terminals. Transmission unit with simple configuration (
Even if the bus is a functional unit, some measures must be taken to prevent the entire bus system from becoming unusable due to a failure in its own station.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to provide an extremely simple configuration suitable for a functional unit with a simple configuration, which is a single transmission unit. An object of the present invention is to provide an abnormality monitoring circuit for a transmission unit for a multi-drop 7-real bus, which can prevent the spread of abnormality.

E. Means for Solving the Problems The abnormality monitoring circuit according to the present invention includes, in a transmission unit that connects a transmission driver to a multi-drop serial bus by wired logic, a switch means for disconnecting the output end of the transmission driver from the bus. , a receiver whose input end is connected to the output end of the transmission driver; a time monitoring circuit that issues an output signal when the received data signal obtained from the receiver remains at an active level for a certain period of time or more; and this circuit means. The apparatus further comprises switch control circuit means for turning off the switch means in response to the output signal of and for turning the switch means back on if the received data signal becomes a fixed level immediately thereafter.

78 action When the bus is fixed at the active level due to some abnormality in the local station or in another station, this abnormality is detected by the time monitoring circuit means after a certain period of time, and the switch control circuit means turns off the switch means. . This disconnects the local station's transmit driver and receiver from the bus. If the cause of the above abnormality is in the transmission system of your own station,
Even if the station is disconnected from the bus, the output of the receiver (the output of the transmission driver) remains at the active level, and in that case, the operation of the own station is stopped with the switch means turned off. If the cause of the above abnormality is in another station, the output of the receiver becomes an immovable level by disconnecting the own station from the bus, and in this case, the switch means is turned back on by the switch control circuit means. In other words, the station continues operating after waiting for the other station with the problem to be disconnected from the bus.

G. Embodiment FIG. 1 shows an embodiment of the abnormality monitoring circuit according to the present invention. In the figure, Zl is a transmission driver consisting of an open collector type inverter, the output end of which is connected to the power supply via a pull-up resistor 14 and to the multidrop serial bus 10 via a relay 12. The station's transmission driver and wired logic are connected.

E2 is a receiver, the input end of which is connected to the connection point between the output end of the transmission driver E1 and the relay 12, and is also connected to the bus 10 via the relay 12.

As will be described later, under normal conditions, the output Q of the D-type flip-flop E7 is at H level, and in response to this output, the relay driver E8 turns on the relays 1-2, and the transmitting driver m1 and the receiver E2 are connected to the bus. 10.

E6 is a retriggerable monostable multivibrator (hereinafter referred to as monomulti), which corresponds to the above-mentioned time monitoring circuit means. That is, this monomulti E6 is triggered at the falling point of the received data signal RD obtained from the 1/seaper E2 to L level, and the output Q becomes L level. After that, if the trigger signal is not continued for a certain period of time or more, the output Q of the monomulti E6 becomes H level (see FIG. 2).

The flip flop E7 above is the output Q of the mono multi E6.
In response to the rise of RD, the logic of the received data signal RD is read. In other words, when the received data signal RD goes to the L level (active level of the bus 10) for a part of time T3 or more, the output Q of the monomulti E6 goes to the H level, and at this time, the flip-flop E7 outputs the L level received data signal RD is read and inverted, its output Q becomes L level, the output of relay driver E8 also becomes L level, and relay I2 is turned off. It is now disconnected from the bus 10.

E4 is a monostable multivibrator (it is not connected to allow retriggering, this is also called a monomulti), and when the reset signal R (described later) is at H level, the AND gate E3
It is triggered by the rising edge of the received data signal RD inputted via , and the output Q goes to H level (output Q goes to L level) for a certain period of time T1.

E5 is a retriggerable monostable multivibrator (hereinafter referred to as monomulti), which is triggered by the rising edge of output Q of monomultiple E4, and produces an L level pulse with width T2 at output Q (see FIG. 2). The pulse of the output Q of the monomulti E5 sets the flip-flop E7 and turns on the relay 12.

To summarize the effects of monomultiple E4 and E5, when the received data signal RD rises, after a certain period of time Tl, L of a certain width T2
A level pulse is generated, which sets the flip-flop E7.

Note that the reset signal R is given from a control system (not shown) and becomes H level for the first time some time T4 after the transmission unit is powered on. Until then, the reset signal R is at L level, and it resets the mono multi 5.15 and flip-flop]11X7, and also resets the A
ND Gate 1! Ban X3.

As shown in the waveform diagram of FIG. 3, the reset signal R is at the L level for a part of the time T4 immediately after the power is turned on, so the flip-flop E7 is reset and the relay 12 is turned off. If the received data signal RD normally goes to H level after the power is turned on, the reset signal R goes to X (level), the mono multi I!
A set pulse is generated, which is set, and relay 12
is turned on and connected to bus 10. Received data signal RD
% does not rise to the R level (there is some abnormality in its own station), the % relay 12 remains off, and this faulty unit is not connected to the bus IO. In this way, when the power is turned on, the own station is checked for a failure, and is connected to the bus 10 only if it is normal.

In the waveform diagram of FIG. 2, in the state on the left side, the received data signal SD is changing normally.

In the center state, the received data signal 8D remains at the L level continuously for time T3. At this point, the monomulti E6 detects an abnormality, the flip-flop 1117 is reset, and the relay 12 is turned off to disconnect it from the bus IO.

If the cause of the abnormality in which the received data signal SD is fixed at the L level for a long time is in the own station, even if the relay 12 is turned off, the signal SD remains at the L level, and therefore the relay 12 also remains off.

If the cause is in another station, by turning off the relay 12, the signal SD of the own station returns to H level.

Then, the flip-flop E7 is set by the action of the monomulti E4 and the monomultiplier E7, and the relay 12 is turned on again.

If the bus 10 returns to the H level during this operation, operation will be resumed as is, and if the bus 10 is still fixed at the L level, one or more operations will be repeated.

H1 Effects of the Invention As explained in detail above, the abnormality monitoring circuit according to the present invention can be configured extremely easily using relays and some logic circuit elements, and moreover, the transmission system (including the transmission driver) can be easily configured. It is possible to reliably prevent failures from spreading to the entire bus system, allowing data transmission to continue between all units.

Therefore, the circuit is suitable for a simple-function transmission unit that does not include a cptr.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an abnormality monitoring circuit according to an embodiment of the present invention, and FIGS. 2 and 3 are waveform diagrams showing the operation of the same circuit. 10...Bus, 12...Relay (switch means),
K6...Retriggerable monostable multivibrator (
time monitoring circuit means), E7...flip-flop (central element of switch control circuit means).

Claims (1)

[Claims] (1) A transmission unit that wire logic connects a transmission driver to a multidrop serial bus, including a switch means for disconnecting an output end of the transmission driver from the bus, and an input end connected to the output end of the transmission driver. a receiver, time monitoring circuit means for generating an output signal when a received data signal obtained from the receiver remains at an active level for a predetermined period of time or more, and a time monitoring circuit means for turning off the switch means in response to an output signal of the circuit means. and switch control circuit means for turning on the switch means if the received data signal becomes an immobile level immediately thereafter.