JPH09233132A - Current loop communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance economy and to facilitate connection by adopting an identical interface for all devices in the case of connecting plural equipments each equipped with a microcomputer so as to reduce quantity of connection wires. SOLUTION: In the current loop communication system among plural equipments each equipped with microcomputer, each device is provided with an interface circuit I composed of a transmission reception changeover switch 2a connected to a communication information output circuit of the microcomputer 1 of each device, a transmission reception changeover switch 2b connected to a ground side, and a photocoupler 3 connected to the communication information input circuit of the microcomputer 1 and bridged over the transmission reception changeover switches 2a, 2b. Then the transmission reception changeover switches 2a, 2b are controlled interlockingly with the microcomputer 1 and the transmission reception changeover switches 2a, 2b of each equipment are connected by two communication lines 4a, 4b. The transmission reception changeover switches 2a, 2b are composed of transistors(TRs).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system using a current loop between a plurality of devices using a microcomputer, and particularly when connecting various devices such as audio devices, the interfaces of all the devices are made equal. ,
The present invention relates to a communication method in which the number of connecting lines is reduced to improve economy and facilitate connection.

[0002]

2. Description of the Related Art A system having a circuit configuration as shown in FIG. 6 is generally used for bidirectional communication for the purpose of mutually controlling a plurality of connected devices by a microcomputer incorporated therein. It is used. That is, in the figure, each device includes a microcomputer 11 and an interface circuit 12, respectively, and the interface circuit 12 includes a photo coupler 13 connected to an information input circuit of the microcomputer 11, and a photo coupler 13 of the photo coupler 13. It has terminals 14a and 14b connected to the input section, a terminal 14c connected to the information output circuit of the microcomputer 11, and a ground terminal 14d. When the device A and the device B are connected to each other, the interface circuits 12a and 12 are used as communication lines between the microcomputers.
b is connected by connection lines 14a, 14b, 14c, 14d.

Now, when sending a signal from device A to device B,
The signal transmitted from the microcomputer 11a on the device A side travels through the connection line 14a, flows to the photocoupler 13b of the device B to transfer information to the microcomputer 11b, and returns to the device A through the connection line 14b. Also, device B
When the signal is transmitted from, the signal is transmitted through the connection lines 14c and 14d.

[0004]

The above-mentioned conventional example shown in FIG. 6 has the drawback that four connecting wires are required, and the cost of the connecting wires and the terminal portion becomes high. In order to solve this drawback, there is an invention described in, for example, Japanese Patent Application Laid-Open No. 1-157153. The present invention, as shown in FIG. 7, includes an interface 111A of a terminal side microcomputer,
It is composed of an interface 111B on the NCU (network control circuit) side and two cable lines (connection lines) connecting the two, and the description of the configuration and operation is omitted. Communication can be activated from both the NCU side and the NCU side.

However, in the connection method described in Japanese Patent Laid-Open No. 1-157153, the interface 111A and the interface 111B have different structures, and the NCU and the microcomputer on the terminal side are in a subordinate relationship.
B must be connected, and if there are various types of equipment, such as an audio system, and the combination differs depending on the user, then it is necessary to equip each equipment with both interfaces, and Interface 111A and interface 111 between the respective devices
It is necessary to connect B in combination, and it is not a suitable communication method in a system that allows general end users who are not experts to connect various types of equipment on the same foot. There was a task to be done.

Therefore, in the present invention, the interfaces of various devices equipped with the microcomputer are all of the same type, and when connecting a plurality of devices, two interfaces of the same type are connected. It is an object of the present invention to provide a current loop communication system between microcomputers which enables bidirectional communication by connecting with a wire and can solve the above-mentioned problems.

[0007]

A current loop communication system according to the present invention for achieving the above object will be described with reference to the reference numerals used in FIG. 1 to FIG. 5 showing an embodiment thereof. According to a first aspect of the present invention, in a current loop communication system between a plurality of devices equipped with a microcomputer, each device includes a transmission / reception changeover switch 2a connected to a communication information output circuit of the microcomputer 1, A transmission / reception changeover switch 2b which is also connected to the ground side
And a photo coupler 3 connected across the communication information input circuit of the microcomputer 1, the transmission / reception changeover switch 2a, and the transmission / reception changeover switch 2b.
And a transmission / reception change-over switch 2b and a transmission / reception change-over switch 2b are controlled by the microcomputer 1 in an interlocking manner, and the transmission / reception change-over switch 2a and the transmission / reception change-over switch 2b of each device are mutually connected Is a current loop communication system characterized by being connected by two communication lines 4a and 4b. A second invention is the current loop communication system according to the first invention, wherein the transmission / reception changeover switch 2a and the transmission / reception changeover switch 2b are transistor switches.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 for explaining a basic configuration of a current loop communication system in a device, and an embodiment using a plurality of devices and an operation thereof, regarding an embodiment of a current loop communication system of the present invention. The principle will be described with reference to FIGS. 2 and 3. In FIG. 1, reference numeral 1 is a microcomputer installed in a device (enclosed by a dashed line) and I is an interface circuit of the present invention (enclosed by a dotted line). Also, 4a and 4b are communication lines that connect the devices to each other.

The interface circuit I includes a transmission / reception changeover switch 2a connected to the communication information output circuit of the microcomputer 1, a transmission / reception changeover switch 2b also connected to the ground side, and a communication information input circuit of the microcomputer 1. And a photo coupler 3 connected across the transmission / reception changeover switch 2a and the transmission / reception changeover switch 2b. Both of the transmission / reception changeover switches are controlled in conjunction with a control signal from the microcomputer 1. In addition, communication lines 4a and 4b for connection with other devices are connected to both the transmission / reception changeover switches 2a and 2b. In this drawing, both switches 2a and 2b are shown as switches as symbols for explaining the principle of the function, but in the implementation, transistor switches are used to control the switching operation by a microcomputer. Has been done.

2 and 3 are diagrams for explaining the configuration and operating principle of the communication system of the present invention using two devices (device A and device B). For convenience of the following description, the microcomputer 1, The reference numerals of the interface circuit I and the like are distinguished by adding a for the device A and b for the device B. In the figure, the device A and the device B have the same configuration, and the device A transmission / reception changeover switch 2aa and the device B transmission / reception changeover switch 2ab, and the device A transmission / reception changeover switch 2ba and the device B transmission / reception changeover switch 2bb.
Are mutually connected by the communication lines 4a and 4b as described above. Also, as the initial condition (in the communication standby state), the device A,
The transmission / reception changeover switches 2aa and 2ba of the device B and the transmission / reception changeover switches 2ab and 2bb of the device B are all turned on to the photocouplers 3a and 3b. That is, when viewed from the microcomputer 1, all are in the off state.

FIG. 2 shows a case of communicating from the device A to the device B. The transmission / reception changeover switch 2aa of the device A is turned on to the communication information output circuit side of the microcomputer 1a, and the transmission / reception changeover switch 2ba is turned on to the ground side. While meanwhile,
Both the transmission / reception changeover switch 2ab and the transmission / reception changeover switch 2bb of the device B are still turned on to the diode side of the photocoupler 3b. The communication information from the microcomputer 1a propagates along the thick arrow and is input to the communication information input circuit of the microcomputer 1b via the photocoupler 3b, and the current loop communication from the device A to the device B is performed.

FIG. 3 shows a case of communicating from the device B to the device A. The transmission / reception changeover switch 2ab of the device B is turned on to the communication information output circuit side of the microcomputer 1b, and the transmission / reception changeover switch 2bb is turned to the ground side. On the other hand, both the transmission / reception changeover switch 2aa and the transmission / reception changeover switch 2ba of the device A are still turned on to the diode side of the photocoupler 3a. Communication information from the microcomputer 1b propagates along the thick arrow, and the photo coupler 3
It is input to the communication information input circuit of the microcomputer 1a via b, and the current loop communication from the device B to the device A is performed.

As described above, in the current loop communication system of the present invention, the interface circuit I has the same structure in any device, and since it is only connected by two communication lines, anyone can use it. You can easily and definitely connect. Communication activation is performed by the microcomputer 1 that transmits information, and complete bidirectional communication is realized by two communication lines.

As described in the section of the embodiment, it is also possible to connect three or more devices on a common bus for mutual communication.

[0015]

Embodiments of the current loop communication system of the present invention will be described below. FIG. 4 shows the configuration of the first embodiment, which is a configuration for implementing the principle diagrams shown in FIGS. The transmission / reception changeover switch 2a and the transmission / reception changeover switch 2b in the principle diagram are both the transistor Tr1 and the transistor Tr2.
aa is Tr1a, and transmission / reception changeover switch 2ba is Tr.
2a, the transmission / reception changeover switch 2ab of the device B is Tr1.
b, the transmission / reception changeover switch 2bb is replaced with Tr2b. The microcomputer 1 and the photo coupler 3 are the same as in the principle diagram.

The operation of the first embodiment will be described. In normal time (when not communicating), the transistors Tr1a and Tr2
a, Tr1b, Tr2b are all off. When the device A wants to transmit, the transistor Tr2a is turned on under the control of the microcomputer 1a. Communication data is performed by turning on / off the transistor Tr1a. The current flowing through the transistor Tr1a is the photocoupler 3a (of the interface Ia) inside the device A.
Then flows through the communication line 4a to the photocoupler 3b (of the interface Ib) inside the device B. The current flowing into the photocoupler 3b returns to the device A through the communication line 4b because the transistor Tr2b is off, and flows to the ground through the transistor Tr2a.

When transmitting from the device B, contrary to the above, the transistor T is controlled by the microcomputer 1b.
Turn on r2b. Communication data is transistor Tr1
This is performed by turning on / off b. The current flowing through the transistor Tr1b flows into the photocoupler 3b (of the interface Ib) inside the device B and the photocoupler 3a (of the interface Ia) inside the device A through the communication line 4a. The current flowing into the photocoupler 3a returns to the device B through the communication line 4b because the transistor Tr2a is off, and flows to the ground through the transistor Tr2b.

When there are three or more devices, if two interfaces I are attached to each device, any one of the two interfaces I may be connected to each other.

FIG. 5 shows the configuration of the second embodiment. A plurality of (four in the figure) devices A, B, C, D, ... Are connected on one bus (4A, 4B). By making such a connection, any device can communicate with other connected devices, and the interface circuit I itself can be provided for each device, and only two connectors can be provided. It is good and cost effective.

In each of the above embodiments, the case where the data is transmitted from either one of the devices has been described.
It may happen that they are transmitted at the same time. In this case, a signal obtained by ORing the respective data flows through the respective photocouplers 3a and 3b, and erroneous data is detected by the respective photocouplers. In this case, the microcomputer can check whether or not the correct data is transmitted (that is, whether or not the other device is transmitting at the same time) by monitoring the signal input from the information input terminal. No trouble occurs.

The embodiments which are considered to be representative of the present invention have been described above. However, the present invention is not necessarily limited to the structures of the embodiments, but has the above-mentioned constitutional requirements according to the present invention, and The present invention achieves the object of the present invention and can be appropriately modified and implemented within the range having the following effects.

[0022]

As is apparent from the above description, in the current loop communication system according to the present invention, the same interface circuit is used for each device in the communication system by the current loop between a plurality of devices using the microcomputer. The two-way connection enables the two-way communication by connecting the interface circuit of each device.
Therefore, it is advantageous in terms of economy.

As described above, making the interface circuits of the respective devices equal and connecting the interfaces of all the devices equally makes it possible for a general end user to connect various devices such as audio devices. It is extremely convenient to handle.

Particularly, when a large number of devices are connected, the above-mentioned economic efficiency and convenience bring about remarkable effects.

As is clear from the above, the current loop communication system of the present invention, when a plurality of devices controlled by a microcomputer are connected to communicate with each other, the interfaces of the respective devices are made equal to each other. Therefore, it is possible to expect an effect that the device can be configured so as to be capable of bidirectional communication and that the device can be economically connected and the convenience of use can be brought about.

[Brief description of drawings]

FIG. 1 is a principle diagram illustrating an operation and a circuit configuration of an embodiment of the present invention.

FIG. 2 is a principle diagram illustrating the operation and configuration of the current loop communication system of the present invention.

FIG. 3 is a principle diagram illustrating an operation and a configuration in the opposite direction of the communication system of the same.

FIG. 4 is a circuit configuration diagram of the first embodiment.

FIG. 5 is a circuit configuration diagram of a second embodiment.

FIG. 6 is a principle diagram illustrating an operation and configuration of a conventional current loop communication system.

FIG. 7 is a circuit diagram illustrating the configuration of an interface circuit transferred from Japanese Patent Application Laid-Open No. 1-157153 as another conventional example.

[Explanation of symbols]

 1 Microcomputer 2a Transmission / reception changeover switch 2b Transmission / reception changeover switch 3 Photocoupler 4a Communication line 4b Communication line

Claims (2)

[Claims] 1. In a current loop communication method between a plurality of devices equipped with a microcomputer, each device has a transmission / reception changeover switch (2a) connected to a communication information output circuit of a microcomputer (1). ), A transmission / reception changeover switch (2b) also connected to the ground side, a communication information input circuit of the microcomputer (1), the transmission / reception changeover switch (2a), and a transmission / reception changeover switch.
(2b) is provided with an interface circuit (I) consisting of a photocoupler (3) connected across, the transmission and reception changeover switch (2a) and the transmission and reception changeover switch (2b) by the microcomputer (1) The transmission and reception changeover switch (2a) and the transmission and reception changeover switch (2b) of each device are controlled in conjunction with each other, and the devices are mutually connected by two communication lines (4a) and communication lines (4b). A current loop communication method characterized by. 2. The current loop communication system according to claim 1, wherein the transmission / reception changeover switch (2a) and the transmission / reception changeover switch (2b) are transistor switches.