CN105629832A

CN105629832A - No-transmit-receive-control-end RS485 transmit-receive automatic switching isolation circuit and method thereof

Info

Publication number: CN105629832A
Application number: CN201510994349.6A
Authority: CN
Inventors: 黄永平; 金玉善
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2015-12-25
Filing date: 2015-12-25
Publication date: 2016-06-01
Anticipated expiration: 2035-12-25
Also published as: CN105629832B

Abstract

The invention discloses a no-transmit-receive-control-end RS485 transmit-receive automatic switching isolation circuit and a method thereof. The automatic switching isolation circuit comprises an MCU, an RXD, a TXD, an ISO1, an ISO2, a U1, a transmit control end and a U2. The MCU is provided with a UART. The RXD arranged on the UART is connected with the RXD arranged on the automatic switching isolation circuit. The TXD arranged on the UART is connected with the TXD arranged on the automatic switching isolation circuit. Signal isolation is performed on the ISO1 and the ISO2 and then the ISO1 and the ISO2 are connected with the TXD end and the RXD end arranged on the automatic switching isolation circuit. The isolated signals of the TXD arranged on the automatic switching isolation circuit are outputted through the fifth pin of the ISO2 to be connected with the transmit control end of the lower part of the U1. The upper part of the U1 receives signals of an RS485 bus, and the signals are outputted from the first pin to be connected with the third pin of the ISO1 and then transmitted to the RXD arranged on the automatic switching isolation circuit through optical isolation. The method of the switching isolation circuit is simple in transmission, and hardware connection and program designing are simplified by the method so that the method is suitable for popularization.

Description

A kind of without transmitting-receiving control end RS485 transmitting-receiving switching isolation circuit and method automatically

Technical field

The present invention relates to and automatically switch isolation circuit technical field, particularly relate to a kind of without transmitting-receiving control end RS485 transmitting-receiving switching isolation circuit and method automatically.

Background technology

Along with the development of digital technique, the system being made up of micro-chip is also day by day complicated, single micro-chip is often difficult to meet requirement, at this moment often to be used multiple micro-chip to form a distributed system, and RS485 bus can be adopted between multiple micro-chip to carry out connecting communication.

On hardware implementing, RS485 is only with two lines, difference signal is adopted to transmit, compared with RS232, the transmission range of RS485 bus is longer, and immunity from interference is stronger, and hardware interface cost is low, link cost between each equipment is also low, and these characteristics are also the major causes using RS485 bus in industrial system.

On software simulating, due to RS485 bus in software design substantially compatible with RS232 bus, its communication software simplicity of design, all micro-chips have UART (universal asynchronous receiving-transmitting device) function, it is possible to realize the design of software easily.

RS458 industrial application is ripe, and a large amount of existing industrial equipmentss all provides RS485 interface, and thus even to this day, RS485 bus industrial also has very important status in applying.

Traditional RS485 bus connects and connects multiple equipment by two lines in bus mode, it is achieved the half-duplex operation communication between each equipment. Utilizing the serial of universal asynchronous receiving-transmitting device UART in microcontroller to send the transmission data end DI of data end TXD connection RS485 driving, serial received data end RXD connects the reception data end RO that RS485 drives. Because RS485 is half-duplex basis work, so when needing to send data, to be controlled RS485 drive as transmission state by setting high direction controlling end TXEN, when needs receive data, RSS485 will be controlled drive as reception state by setting low direction controlling end TXEN. Traditional mode of connection of MCU and RS485 driving part adopts three line (TXD, RXD, TXEN) connect, MCU will according to be send data, or receive data, must in suitable data direction control end TXEN, could ensure reliably to communicate, when software programming, carry out controlling party to control end TXEN by program, send data to determine or receive data, and could to revise TXEN after requiring transmission to terminate be reception state. And during general serial line interface programming, the data sent and the data of reception are not bytes, but data one by one, data are generally put in queue, by interrupting fetching data transmission from transmit queue, or it is put in receiving queue by interrupting receive data, and at this moment upper level applications needs to know that frame data have been sent completely, reception state could be converted to by direction of passage control end TXEN, whether low layer queue is empty state to require upper layer application to check, or, low-level communication storehouse does not just provide the function checking queue sometimes. So being generally adopt the method for time delay to address this problem, it is believed that after time delay to certain time, a frame is sent completely, and at this moment just makes direction controlling end TXEN be converted to reception state. And time delay too long time, the other side may send reply data, it is possible to does not receive data. So the other side's delivery time also to be carried out time delay adjustment according to transmission side, it is not good to adjust, it is possible to communication can be made unstable, bad during communication fashion.

So when tradition RS485 communicates, adjustment control TXEN direction of travel switch instant, is that influential system communicates stable factor, will adjust according to realization communication speed, line length and device responds time, otherwise system communication will be unreliable. In this kind of mode, how long being turned into reception state after also being considered to send in program, this time delay to be adjusted according to realization communication speed, line length and device responds time, very inconvenient.

Summary of the invention

Based on the technical problem that background technology exists, the present invention proposes a kind of without transmitting-receiving control end RS485 transmitting-receiving switching isolation circuit and method automatically.

The one that the present invention proposes receives and dispatches switching isolation circuit automatically without transmitting-receiving control end RS485, comprise MCU, RXD, TXD, ISO1, ISO2, U1, transmission control end and U2, described MCU is provided with UART, RXD on described UART is connected to switching automatically and isolates the RXD on circuit, TXD on described UART is connected to switching automatically and isolates the TXD on circuit, after described ISO1 and ISO2 carries out signal isolation, it is connected to switching automatically and isolates the TXD end on circuit and RXD end, the signal of TXD on described automatic switching isolation circuit after isolation exports through 5 pin of ISO2, it is connected to the transmission control end of U1 lower part, the upper part of described U1 receives the signal in RS485 bus, export from 1 pin, it is connected to 3 pin of ISO1, being sent to switching automatically after light is isolated isolates on the RXD on circuit, it is connected in outside RS485 bus on the right side of described U1, described U2 is the conversion of 5V/5V isolated from power, for isolated from power inside and outside power supply.

Preferably, described U1 is that RS485 drives device.

The invention allows for a kind of method receiving and dispatching switching isolation circuit automatically without transmitting-receiving control end RS485, the method of described automatic switching isolation circuit comprises transmission data TXD and receives data RXD, described transmission data TXD concrete steps are as follows: when TXD does not send data, TXD is high level, and when sending data, it may be that 1 also may be 0; When TXD sends 1, the photodiode not conducting of ISO2, the phototriode pipe cut-off in ISO2,5 pin in ISO2 are lower level, and the transmitting portion making U1 following exports forbids, it exports as high resistance state, by R3 and R6 two resistance, make RS485 transmit 1; When TXD sends 0, the photodiode conducting of ISO2, phototriode conducting in ISO2,5 pin in ISO2 are high level, the transmitting portion making U1 following allows, and its output is determined by 4 pin connected, and the 4 pin ground connection of U1, so it is 0 that the following transmitting portion of U1 exports, also it is exactly make RS485 transmit difference signal to transmit 0;

Described reception data RXD comprises reception mode and TXD always and controls reception mode, the described mode that always receives is when in the 0 ohmic resistance welding of R4, and R5 is not when welding, also it is exactly the 2 pin ground connection of U1, reception part in U1 top is allowed always, then the data in RS485 bus can receive always, and the data oneself sent can also receive, and can be used for oneself checking in software; Described TXD control reception mode is not for welding as R4, and TXD control when the 0 ohmic resistance welding of R5 is upper, after the reception part light isolation of U1 top, making when TXD sends data, RXD always 1, does not namely receive data, and RS485 bus is when carrying out data, RXD can receive data.

Preferably, when described TXD exports 1, RS485 driver output is 1, TXD when exporting 0, RS485 driver output 0; When TXD does not send data, TXD output is 1, RS485 output is 1.

Preferably, when TXD sends 1,5 pin of ISO2 are lower level, and control U1 top reception part receives permission, RS485 bus signals is 1, so 1 pin of U1 exports as high level, then the light emitting diode not conducting of ISO1, then corresponding phototriode pipe cut-off, R1 pull-up resistor, makes RXD be 1; When TXD sends 0,5 pin of ISO2 are high level, and control U1 top receives part reception and forbids, 1 pin of U1 exports as high resistance state, then the light emitting diode also not conducting of ISO1, then corresponding phototriode pipe also ends, and R1 pull-up resistor, makes RXD be 1.

Preferably, when outside RS485 bus carrys out data 1, now TXD does not send data, and TXD is 1, the receptor of U1 top allows, making RXD be received as 1, when outside RS485 bus carrys out data 0, the receptor of U1 top allows, 1 pin of U1 exports as lower level, the then light emitting diode conducting of ISO1, corresponding phototriode pipe conducting, makes RXD be 0.

In the present invention, by adopt present method, eliminate tradition RS485 bus communication in transmit and receive direction controlling end TXEN pin, when programming, need not considering that TXEN turns to moment problem, the present invention can realize being automatically converted to reception state after frame data are sent completely. Improve programming and debugging efficiency, time and the programming time of general program routine are suitable, it is possible to improve the efficiency of nearly more than 50%. Improve the reliability of system communication simultaneously.

By removing TXEN end, also save part hardware resource, simplify PCB design.

The interference of system is inevitable in industrial environment, by adding Phototube Coupling and isolated from power, too increases the reliability of system communication. By this process simplify signal wiring and programdesign, it is applicable to promoting.

Accompanying drawing explanation

Fig. 1 is a kind of schematic circuit receiving and dispatching switching isolation circuit automatically without transmitting-receiving control end RS485 that the present invention proposes.

Embodiment

Below in conjunction with specific embodiment, the present invention done further explanation.

In the present invention, when described TXD exports 1, RS485 driver output is 1, TXD when exporting 0, RS485 driver output 0; When TXD does not send data, TXD output is 1, RS485 output is 1. When TXD sends 1,5 pin of ISO2 are lower level, and control U1 top reception part receives permission, RS485 bus signals is 1, so 1 pin of U1 exports as high level, then the light emitting diode not conducting of ISO1, then corresponding phototriode pipe cut-off, R1 pull-up resistor, makes RXD be 1; When TXD sends 0,5 pin of ISO2 are high level, and control U1 top receives part reception and forbids, 1 pin of U1 exports as high resistance state, then the light emitting diode also not conducting of ISO1, then corresponding phototriode pipe also ends, and R1 pull-up resistor, makes RXD be 1. When outside RS485 bus carrys out data 1, now TXD does not send data, TXD is the receptor of 1, U1 top is allow, and makes RXD be received as 1, when outside RS485 bus carrys out data 0, the receptor of U1 top allows, and 1 pin of U1 exports as lower level, then the light emitting diode conducting of ISO1, corresponding phototriode pipe conducting, makes RXD be 0.

In the present invention, RS485 is industry standard communication bus, it is possible to connecting multiple devices with bus connecting mode, its implementation cost is low, extensively in Industry Control equipment. Present invention achieves a kind of RS485 bus communication circuitry that do not need transmitting-receiving control end, that automatic transceiving turns to.

The above; it is only the present invention's preferably embodiment; but protection scope of the present invention is not limited thereto; any it is familiar with those skilled in the art in the technical scope that the present invention discloses; technical scheme and invention design thereof according to the present invention are equal to replacement or are changed, and all should be encompassed within protection scope of the present invention.

Claims

1. receive and dispatch switching isolation circuit automatically without transmitting-receiving control end RS485 for one kind, it is characterized in that, comprise MCU, RXD, TXD, ISO1, ISO2, U1, transmission control end and U2, described MCU is provided with UART, RXD on described UART is connected to switching automatically and isolates the RXD on circuit, TXD on described UART is connected to switching automatically and isolates the TXD on circuit, after described ISO1 and ISO2 carries out signal isolation, it is connected to switching automatically and isolates the TXD end on circuit and RXD end, the signal of TXD on described automatic switching isolation circuit after isolation exports through 5 pin of ISO2, it is connected to the transmission control end of U1 lower part, the upper part of described U1 receives the signal in RS485 bus, export from 1 pin, it is connected to 3 pin of ISO1, being sent to switching automatically after light is isolated isolates on the RXD on circuit, it is connected in outside RS485 bus on the right side of described U1, described U2 is the conversion of 5V/5V isolated from power, for isolated from power inside and outside power supply.

2. according to claim 2 a kind of without transmitting-receiving control end RS485 transmitting-receiving switching isolation circuit and method automatically, it is characterised in that, described U1 is that RS485 drives device.

3. receive and dispatch the method for switching isolation circuit automatically without transmitting-receiving control end RS485 for one kind, it is characterized in that, the method of described automatic switching isolation circuit comprises transmission data TXD and receives data RXD, described transmission data TXD concrete steps are as follows: when TXD does not send data, TXD is high level, and when sending data, it may be that 1 also may be 0; When TXD sends 1, the photodiode not conducting of ISO2, the phototriode pipe cut-off in ISO2,5 pin in ISO2 are lower level, and the transmitting portion making U1 following exports forbids, it exports as high resistance state, by R3 and R6 two resistance, RS485 is made to transmit difference signal 1; When TXD sends 0, the photodiode conducting of ISO2, phototriode conducting in ISO2,5 pin in ISO2 are high level, the transmitting portion making U1 following allows, and its output is determined by 4 pin connected, and the 4 pin ground connection of U1, so it is 0 that the following transmitting portion of U1 exports, also it is exactly make RS485 transmit difference signal 0;

Described reception data RXD comprises reception mode and TXD always and controls reception mode, the described mode that always receives is when in the 0 ohmic resistance welding of R4, and R5 is not when welding, also it is exactly the 2 pin ground connection of U1, reception part in U1 top is allowed always, then the data in RS485 bus can receive always, and the data oneself sent can also receive, and can be used for oneself checking in software; Described TXD controls reception mode for not welding as R4, and time in the 0 ohmic resistance welding of R5, TXD control after the reception part light isolation of U1 top, make when TXD sends data, RXD always 1, namely the data oneself sent are not received, and when outside RS485 bus carrys out data, RXD can receive data.

4. according to claim 3 a kind of receive and dispatch switching isolation circuit and method automatically without transmitting-receiving control end RS485, it is characterised in that, when described TXD exports 1, RS485 driver output is 1, TXD when exporting 0, RS485 driver output 0; When TXD does not send data, TXD output is 1, RS485 output is 1.

5. according to claim 3 a kind of without transmitting-receiving control end RS485 transmitting-receiving switching isolation circuit and method automatically, it is characterized in that, when TXD sends 1,5 pin of ISO2 are lower level, and control U1 top reception part receives permission, RS485 bus signals is 1, so 1 pin of U1 exports as high level, then the light emitting diode not conducting of ISO1, then corresponding phototriode pipe cut-off, R1 pull-up resistor, makes RXD be 1; When TXD sends 0,5 pin of ISO2 are high level, and control U1 top receives part reception and forbids, 1 pin of U1 exports as high resistance state, then the light emitting diode also not conducting of ISO1, then corresponding phototriode pipe also ends, and R1 pull-up resistor, makes RXD be 1.