CN203445871U - RS485 communication circuit - Google Patents

The utility model discloses an RS485 communication circuit. The RS485 communication circuit includes a differential transceiver (U1), a PNP triode (P1), a first resistor (R11), a second resistor (R12), a third resistor (R13) and a fourth resistor (R10); one end of the first resistor (R11) is connected with the collector of the PNP triode (P1); a serial port receiving enable end (RE) of the differential transceiver is connected with a serial port transmitting enable end (DE); the other end of the first resistor (R11) is grounded; the base of the PNP triode (P1) is connected with one end of the fourth resistor (R10); the other end of the fourth resistor (R10) is connected with a transmitting end (TXD) of an instrument terminal; the emitter of the PNP triode (P1) is connected with a work power supply; a serial port receiving end of the differential transceiver (U1) is connected with a receiving end (RXD) of the instrument terminal; a serial port transmitting end (D) of the differential transceiver (U1) is grounded; a differential signal line negative end (B) of the differential transceiver (U1) is connected with one end of the second resistor (R12); a differential signal line positive end (A) of the differential transceiver (U1) is connected with one end of the third resistor (R13); the other end of the second resistor (R12 ) is connected with the work power supply; and the other end of the third resistor (R13) is grounded. With the RS485 communication circuit adopted, when the triode P1 is damaged, and an entire terminal RS485 communication interface is in a receiving state, and an RS485 bus will not be influenced.

A kind of RS485 communicating circuit

Technical field

The utility model belongs to a kind of communicating circuit, especially a kind of RS485 communicating circuit.

Background technology

In power electronic equipment, often need in severe electric power environmental, carry out telecommunication, RS485 has become first-selected communication modes.RS485 communication is generally applied in half duplex communication, carves and only allows an equipment to main frame transmitted signal at a time, and other equipment must be in accepting state, and the order all devices that main frame issues all can receive.If the some time carves an existing above equipment simultaneously to main frame transmitted signal, just there will be signal stack, main frame is can not receive correct data, communication meeting is failure always.

Apply at the scene in the process of RS485 networking, when running into, communication is not gone up, during unresponsive situation, and most cases is because certain station terminal RS485 circuit in networking damages, and causes whole RS485 bus paralysis, at this moment must change terminal, could recover network normal.

The model of chip U1 is SN65HVD3082ED, and its truth table is:

But when in Fig. 1, NPN triode N1 damages, RS485 chip U1 can export low always, i.e. differential voltage U between pin A and pin B _aBbe low level always, make the paralysis of RS485 bus.

Utility model content

In order to solve the problem that extremely causes the paralysis of RS485 bus due to separate unit terminal RS485 drives triode, a kind of RS485 communicating circuit is now proposed.

This circuit comprises difference transceiver U1, PNP triode P1, the first resistance R 11, the second resistance R 12, the 3rd resistance R 13 and the 4th resistance R 10, the collector electrode of one end of the first resistance R 11 and PNP triode P1 wherein, the serial ports of difference transceiver receives Enable Pin RE and is connected with serial ports transmission Enable Pin DE, other end ground connection, the base stage of PNP triode P1 is connected with one end of the 4th resistance R 10, the other end of the 4th resistance R 10 connects the transmitting terminal TXD of instrument terminal, the emitter of PNP triode P1 connects working power, the serial ports receiving terminal of difference transceiver U1 connects the receiving terminal RXD of instrument terminal, serial ports transmitting terminal D ground connection, the differential signal line negative terminal B of difference transceiver U1 connects one end of the second resistance R 12, differential signal line anode A connects one end of the 3rd resistance R 13, the other end of the second resistance R 12 connects working power, the other end ground connection of the 3rd resistance R 13, differential signal line anode A and differential signal line negative terminal B are the output of this RS485 communicating circuit.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of existing RS485 control circuit;

Fig. 2 is schematic diagram of the present utility model.

Embodiment

Below in conjunction with accompanying drawing, also with best embodiment, the utility model is described in detail.

The technical program adopts and to realize RS485 half duplex communication circuit as Fig. 2 principle.

This circuit comprises difference transceiver U1, PNP triode P1, the first resistance R 11, the second resistance R 12, the 3rd resistance R 13 and the 4th resistance R 10, the collector electrode of one end of the first resistance R 11 and PNP triode P1 wherein, the serial ports of difference transceiver receives Enable Pin RE and is connected with serial ports transmission Enable Pin DE, other end ground connection, the base stage of PNP triode P1 is connected with one end of the 4th resistance R 10, the other end of the 4th resistance R 10 connects the transmitting terminal TXD of instrument terminal, the emitter of PNP triode P1 connects working power, the serial ports receiving terminal R of difference transceiver U1 is connected to the receiving terminal RXD of instrument terminal, serial ports transmitting terminal D ground connection, the differential signal line negative terminal B of difference transceiver U1 connects one end of the second resistance R 12, differential signal line anode A connects one end of the 3rd resistance R 13, the other end of the second resistance R 12 connects working power, the other end ground connection of the 3rd resistance R 13, differential signal line anode A and differential signal line negative terminal B are the output of this RS485 communicating circuit.

In transmission phase, this circuit provides anti-phase driving (TXD is output as low level, and the PIN3 of U1 and PIN4 are high level) by the 4th resistance R 10, PNP triode P1, the first resistance R 11, controls difference transceiver U1 and outwards sends differential level signal; In the reception stage, this circuit provides anti-phase driving by the 4th resistance R 10, PNP triode P1, the first resistance R 11, and (TXD is output as low level, and the PIN3 of U1 and PIN4 are high level), control difference transceiver U1 and receive differential input signal, change non-equilibrium serial ports input signal.When P1 damages, because there is R11 to pull down to ground, making RE is effective condition, and whole terminal RS485 communication interface, in accepting state, can not impact RS485 bus.

When instrument terminal is during in output state, if instrument terminal output high level (TXD output is high), RE is low effectively, and now RS485 bus, by the upper drop-down effect of pin A and pin B, makes the differential voltage U between pin A and pin B _aBfor high level, instrument terminal is to RS485 bus output high level; If terminal is output as low level (TXD is output as low), DE is effectively high, and pin D is low level, the differential voltage U between pin A and pin B _aBfor low level, terminal is to RS485 bus output low level.

When terminal is during in accepting state, TXD is high at idle pulley, and RE is low effectively, if now RS485 bus has data to send to terminal, and terminal energy automatic reception RS485 bus data.

Chip U1 signal is SN65HVD3082ED, and its pinout is as following table:

Chip U1 model is SN65HVD3082ED, and its truth table is:

Above embodiment is more preferably embodiment a kind of of the utility model, and the common variation that those skilled in the art carry out within the scope of the technical program and replacing should be included in protection range of the present utility model.

1. a RS485 communicating circuit, comprise difference transceiver (U1), PNP triode (P1), the first resistance (R11), the second resistance (R12), the 3rd resistance (R13) and the 4th resistance (R10), the collector electrode of one end of the first resistance (R11) and PNP triode (P1) wherein, the serial ports of difference transceiver (U1) receives Enable Pin (RE) and is connected with serial ports transmission Enable Pin (DE), other end ground connection, the base stage of PNP triode (P1) is connected with one end of the 4th resistance (R10), the other end of the 4th resistance (R10) connects the transmitting terminal (TXD) of instrument terminal, the emitter of PNP triode (P1) connects working power, the serial ports receiving terminal of difference transceiver (U1) connects the receiving terminal (RXD) of instrument terminal, serial ports transmitting terminal (D) ground connection, the differential signal line negative terminal (B) of difference transceiver (U1) connects one end of the second resistance (R12), differential signal line anode (A) connects one end of the 3rd resistance (R13), the other end of the second resistance (R12) connects working power, the other end ground connection of the 3rd resistance (R13), differential signal line anode (A) and differential signal line negative terminal (B) are the output of this RS485 communicating circuit.