Description of RS232/RS485/rs422 Interface Converter

Description of RS232/RS485/rs422 Interface Converter

 

The DMUs series converter is a standard RS232/RS485/rs422 converter that completes the electrical conversion between the serial RS232 and RS485/rs422, and can extend the maximum communication distance to 1200 meters (4000 feet ).

DMUs adopt the basic three-line system (txd, rxd, Gnd). No software driver is required for use. The product adopts industrial-level product design (applicable temperature range:-40 ℃ ~ + 85 ℃), including static electricity release protection, with lightning protection function, suitable for various industrial and civil applications.

I. Principles

RS232 interface is a communication protocol for close distance (up to 30-60 meters), slow speed, point-to-point communication. In RS232, only one signal line is used for a signal and the local voltage reference method is adopted, therefore, after long-distance transmission, the voltage at the sender and receiver is different, which may cause communication errors or speed reduction.

RS485/422 interfaces use different methods: Each signal is transmitted by twisted pair wires (two signal lines), and the voltage difference between the two lines is used to represent digital signals. For example, if one of the twisted wires is labeled a (positive) and the other is labeled B (negative), when a is a positive voltage (usually + 5 V ), when B is a negative voltage (usually 0), it indicates the signal "1"; otherwise, A is a negative voltage, and B is a positive voltage, it indicates the signal "0 ". RS485/422 allows a communication distance of 1200 meters, and a suitable circuit can achieve a transmission rate of 2.5 Mb/s.

Rs422 and RS485 adopt the same communication protocol, but there are some differences: rs422 is usually used as an extension of RS232 communication. It uses two twisted pair wires, and data can be transmitted in two directions at the same time (Full Duplex ). RS485 adopts a twisted pair cable, and the input and output signals cannot be simultaneously performed (Half Duplex). RS485 can be used for multi-point communication. Multiple devices can be connected to one signal line. It usually adopts the main/slave structure.

In the DM series converter, only three lines of the COM port are used: txd, rxd, And Gnd (these are the 3, 2, and 5 ports of the D Interface respectively ), txd is the signal input line, rxd is the signal output line, And Gnd is the ground.

In RS485 (Half Duplex) Communication, the RS232 signal output by txd is output by the transmitter (A and B) and converted to RS485 signal, the RS485 signal is received by the receiver (A and B) and converted to the RS232 signal, and sent to rxd.

In rs422 (full-duplex) Communication, two twisted wires are required to transmit the input and output signals because the input and output signals are separated, marked as A, B, Y, Z (A is the positive pole of the input signal, B is the negative pole of the input signal, Y is the positive pole of the output signal, z is the negative pole of the output signal ). When a signal is sent, the RS232 signal output by txd is output by the transmitter (A and B) and converted to the RS485/rs422 signal. When receiving the signal, the RS485/rs422 signal is received by the receiver (Y and Z) and then sent to the serial rxd.

Figure 1: Schematic diagram of DM series RS232/RS485/rs422 Interface Converter (Half Duplex)

Figure 2 DM series RS232/RS485/rs422 Interface Converter schematic (Full Duplex)

Ii. Typical connection method

A maximum of 256 RS485 interfaces can be connected at the output end of DMUs. The typical connection method is 3 (Half Duplex) and 4 (Full Duplex. On the two farthest terminals, each input and output must be connected with a 120 ohm resistor. When the RS485/rs422 interface is connected, the output end of interface A is connected to the input end of interface B, the positive and negative ends of twisted pair wires are connected to the negative ends, and the input end of interface A is connected to the output end of interface B, the positive and negative ends of twisted pair wires are connected to the positive and negative ends.

Figure 2 Typical dm485h (Half Duplex) Method

Figure 4 typical dm485f (Full Duplex) Method

Iii. Specific applications

One end of the DMUs series converter is a 9-core D interface, which can be directly connected to the RS232 standard interface. The other end is the terminal, that is, the RS485/rs422 interface. Two groups of pins are used in the terminal of RS485 interface (Half Duplex): two groups of inputs (B, A, two groups of internal transient connections, system expansion ). The converter is connected to the RS232 standard serial port through the D interface and the RS485 interface through the connection terminal. Three pins are used in the terminal blocks of the rs422 interface (Full Duplex): A group of outputs (Y, Z), two sets of inputs (B, A, two groups of internal transient connections, extension ). The converter is connected to the RS232 standard serial port through the D interface, and to the RS485/rs422 interface through the connection terminal.

Figure 5: Application wiring diagram of dm485h

Figure 6: Application wiring diagram of dm485f

Iv. Notes

1. Twisted Pair wires must be used for long-distance transmission.

2. When multiple terminals are transmitted, the input and output ends of the two terminals are connected with a resistance of 120 Ohm.

Description of RS232/RS485/rs422 Interface Converter