JPH01221952A - Transmission circuit of multidrop system - Google Patents

Abstract

PURPOSE:To perform normal communication between another slave unit and a master unit when short-circuit is generated in a transmission circuit by separating a faulty slave unit automatically. CONSTITUTION:When short-circuit is generated due to the fault of the transmission circuit 6 of the slave unit 2A, transmission output goes to a low level by the malfunction of a microcomputer 7. The master unit 1 judges the generation of the short-cuit of a signal line 3, and supplies a power source for driving a relay via a separation line 16. A photocoupler 14 is energized, and a relay 10 is turned ON, and its normally closed contact 10b is opened, then, the transmission circuit 6 of the slave unit 2A is separated from a signal line 4. The relay 10 is self-held by its normally open contact 10a. When the normally closed contact 10b is opened, the level of the positive side signal line 3 is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-drop transmission circuit in which a plurality of slave units are connected in parallel to a base unit via two signal lines.

[Prior Art] As this type of transmission circuit, one shown in FIG. 3, for example, is conventionally known. In FIG. 3, 1 is the main unit, 28, 2B, 2C, . . . are slave units, and 3 and 4 are the base unit 1 and slave units 2A, 28.2C, . These are positive side and negative side signal lines, respectively. Handset 2A,
2B, 2G, .
It is composed of a microcomputer 7 that controls the. 8 is the input resistance of the receiving circuit 5, 9 is the signal line and the slave unit 2A
This is a branch line that connects the receiving circuit 5 and the transmitting circuit 6.

Here, from base unit 1 to slave units 2A to 2C or slave units 2A to
Communication from 2C to base unit 1 is performed by sharing two signal lines 3 and 4. Although not shown, a plurality of slave units similarly use the same signal lines 3 and 4.

[Problems to be Solved by the Invention] Therefore, if the transmitting circuit 6 of one handset, for example 2A, is short-circuited for some reason, or the microcomputer 7 of the handset 2A malfunctions, the transmission output may turn on. If it remains as it is, that is, remains at the L level, not only the failed handset 2A but also other handsets connected to the common signal lines 3 and 4 will be short-circuited.

As a result, the base unit 1 and all slave units 2A, 2B, 2C, .
...Communication between the two becomes impossible. This state continues until the short-circuited handset 2A is found and the handset 2A is artificially disconnected from the signal lines 3 and 4.

In addition, when searching for the handset 2A that is short-circuited, you have to go through all the handsets 2A, 2B, 2G, etc. one by one, which is very time-consuming. Ta.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to automatically disconnect a malfunctioning handset in a multi-drop transmission circuit when the transmitting circuit of the handset is short-circuited or due to a malfunction of the microcomputer of the handset. Accordingly, it is an object of the present invention to provide a transmission circuit that allows normal communication between other slave units and a base unit.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a multi-drop transmission system in which a plurality of slave units are connected in parallel to a base unit via two signal lines. In the circuit, a contact inserted between the output end of each transmission circuit of the plurality of slave units and one of the signal lines, and connected to the output end of each transmission circuit of the plurality of slave units,
A control circuit for controlling the drive of the contacts, a separation line disposed between the control circuit and the base unit, a means provided in the base unit for detecting the signal state of one signal line, and a means provided in the base unit for detecting the signal state of one signal line. The present invention is characterized by comprising means for supplying power for driving the control circuit from the base unit to the separation line when a predetermined signal state is detected by the detection means.

[Function] In the present invention, the output end of the transmitting circuit can be separated from the one signal line by a contact inserted between the output end of the transmitting circuit of the slave unit and one of the signal lines, and this The contacts are driven by a contact drive control circuit connected to the output end of the transmission circuit and a power source for driving the contact drive control circuit supplied from the parent device via a separation line. The main device monitors the signal state of the signal line, and supplies power from the above-mentioned driving power source to the disconnection line when a signal state indicating a short circuit in the transmitting circuit is detected.

Therefore, according to the present invention, in a multi-drop transmission circuit, when a signal line is short-circuited due to a failure in a slave unit, the failed slave unit is automatically disconnected from the signal line, so that the remaining Communication can be continued between the normal child device and the parent device.

Moreover, in the present invention, a contact drive circuit connected to the output end of the transmitting circuit and a contact drive circuit supplied from the base unit via the disconnection line perform the operation of the contact for disconnecting the failed slave unit from the signal line. Since this is done using the power supply, even if the microcomputer or the like of the slave unit malfunctions, the master unit can forcibly disconnect the malfunctioning slave unit.

Furthermore, in the present invention, since communication is not possible with the disconnected slave device, it is possible to identify which slave device is a malfunctioning slave device on the base device side, thereby making it easy to repair the malfunction.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the present invention. FIG. 2 shows a timing chart for explaining the operation in this embodiment.

In FIG. 1, a normally closed contact 10b of a relay IO is connected between the branch line 9 and the human resistance 8 of the receiving circuit 5. A Zener diode 11 is connected between the connection point between this contact 10b and the resistor and the output end of the transmitting circuit 6. Transmission circuit 6
An output resistor 12 is connected to the output terminal of.

The output end of the transmitting circuit 6 is connected to the relay drive circuit 13 to energize the light emitting diode 14a forming the photocoupler 14. This light emitting diode 14a is connected to a separation line 16 via a protection resistor 15. The separation line 16 is connected to the base unit 1 so that power for driving the light emitting diode 14a is supplied from the base unit 1. A relay 10 is connected in series with the phototransistor 14b on the light receiving side of the photocoupler 14.
, and also in parallel, the normally open contact 10a of the relay 10 is connected in a self-holding manner.

The main unit 1 monitors the level state of the positive side signal line 3, and when it is detected that the level is low and has become a veil, and the detected state continues for a predetermined period of time or more,
A predetermined power supply for driving the relay is supplied to the separation line 16.

When the transmitter circuit 6 of the slave unit 2^ outputs a low level (OO), the output of the transmitter circuit 6 of the other slave units 2B, 2G, etc. is transmitted through the branch line 9 as shown in FIG. Such a low level also appears on the end and positive side signal lines 3. At the same time,
The relay drive circuit 13 of the slave unit 2A operates to turn on the light emitting diode 14a of the photocoupler 14, but since relay drive power is not supplied from the base unit 1 via the disconnection line 16, the relay drive circuit 13 in FIG. As shown in photocoupler 1
4. Therefore, relay 10 does not turn on.

On the other hand, as shown in FIG. determines that a short circuit has occurred in the signal line 3, and supplies power for driving the relay via the disconnection line 16, as shown in FIG. As a result, the photocoupler 14 is energized, the relay IO is turned on, and its normally closed contact 10b is opened, thereby disconnecting the transmitting circuit 6 of the handset 2A from the signal line 4. Since the relay IO is self-maintained by its normally open contact 10a, the supply of power for driving the relay only needs to be temporary.

When the relay IO is turned on and its normally closed contact 10b is opened, the level of the positive signal line 3 is restored as shown in FIG.

On the other hand, when a low level continues to occur on the branch line 9 of the handset 2A, a low level also appears as faM on the branch line 9 of other handsets (for example, 2B) that are not short-circuited, but the low level is blocked by the Zener diode 11 and is not input to the relay drive circuit 13. Therefore, this relay drive circuit 13 does not drive the photocoupler 14 and, as a result, does not operate to turn on the relay 10. , its normally closed contact 10b remains closed, and the transmitting circuit 6 of the handset 2B is not disconnected from the signal line 3.

In addition, relay 1 in handset 2A, 2B, 2G,...
As described above, the self-holding circuit using the 0 contact 10a is self-held in the slave unit where the failure has occurred, but it is released by turning off the power to check the failure of the slave unit. However, if you set the reset switch to relay 1
Of course, it may be inserted in series with the 0 coil and reset by opening the switch.

[Effects of the Invention] As is clear from the above, according to the present invention, in a multi-drop transmission circuit, when a signal line is short-circuited due to a failure in a slave unit, the failed slave unit automatically Since it is disconnected from the signal line immediately, communication can continue between the remaining normal slave units and the base unit.

Moreover, in the present invention, a contact drive circuit connected to the output end of the transmitting circuit and a contact drive circuit supplied from the base unit via the disconnection line perform the operation of the contact for disconnecting the failed slave unit from the signal line. Since this is done using the power supply, even if the microcomputer or the like of the slave unit malfunctions, the master unit can forcibly disconnect the malfunctioning slave unit.

Furthermore, in the present invention, since communication is not possible with the disconnected slave device, the parent device can identify which slave device is at fault, making it easy to repair the malfunction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a multi-drop control circuit according to the present invention, FIG. 2 is a timing chart of a transmission circuit according to the present invention, and FIG. 3 is a block diagram of an example of a conventional multi-drop control circuit. 1... Base unit, 2A, 2B, 2C,...... Child unit, 3... Positive side signal line, 4... Negative side signal line, 5... Receiving circuit, 6... - Transmission circuit, 7... Microcomputer, 8... Human resistance, 9... Branch line, 10... Relay, 10a... Normally closed contact, 10b... Normally closed contact, 11... - Zener diode, 12... Output resistor, 13... Relay drive circuit, 14... Photocoupler, 14a... Light emitting diode, 14b... Phototransistor, 15... Protection resistor, 16...・Separation line. 7. Invention Im Tongue Circuit Queeninck Dou Yato Diagram 2

Claims (1)

[Scope of Claims] 1) In a multi-drop transmission circuit in which a plurality of slave units are connected in parallel to a base unit via two signal lines, an output terminal of each transmission circuit of the plurality of slave units; and one of the signal lines; and a contact connected to the output end of each transmission circuit of the plurality of slave units;
a control circuit for controlling the drive of the contact; a separation line disposed between the control circuit and the base unit; a means provided on the base unit for detecting a signal state of the one signal line; and means provided in the base unit for supplying power for driving the control circuit from the base unit to the separation line when a predetermined signal state is detected by the detection means. Multi-drop transmission circuit.