Serial interface RS-232, RS422, RS485 definition

Serial interface RS-232, RS422, RS485 definition

The serial interface includes RS-232, RS422, RS485, etc. according to electrical standards and protocols. We have used these serial interfaces for the communication of equipment. We will introduce these interfaces as follows.

One: RS-232

RS-232 is a serial physical interface standard developed by Electronic Industries Association (EIA). The RS-232 bus standard has 25 signal lines, including a main channel and an auxiliary channel. In most cases, the main channel is used. For general duplex communication, only a few signal lines are required, such as a transmission line. A receiving line and a ground line.

DB9

1 DCD carrier detection

2 RXD receive data

3 TXD send data

4 DTR data terminal ready

5 SGND signal ground

6 DSR data ready

7 RTS request to send

8 CTS Clear Send

9 RI ring alert

1 Ground

2 TXD send data

3 RXD receive data

4 RTS request to send

5 CTS Allowed to Send

6 DSR data ready

7 SG signal ground

8 DCD carrier detection

9 send back (+)

10 undefined

11 Data Transmission (-)

12~17 not defined

18 Data Reception (+)

19 Undefined

20 Data Terminal Ready DTR

21 Undefined

22 Ringing RI

23~24 not defined

25 Receive Return (-)

II: RS422

RS422 is a double-ended line transmission signal, through the transmission line driver, the logic level is converted into a potential difference, through the transmission line receiver, the potential difference is converted into a logic level, and the terminal receives information. The RS422 and RS485 circuit principles are basically the same. They are all sent and received in differential mode and do not require digital ground. Differential operation is the root cause of the transmission distance in the same speed condition. RS422 can transmit and receive data in full duplex without affecting each other through the two pairs of twisted pair. RS485 can only work in half duplex, and the sending and receiving cannot be performed at the same time, but only Need a twisted pair.

Three: RS485

RS-485 is based on RS-422, so many RS-485 electrical specifications are similar to RS-422. If you use balanced transmission, RS-485 can use two-wire and four-wire, two-wire system can achieve true multi-point two-way communication.

RS-485, like RS-422, has a maximum transmission distance of approximately 1219 meters and a maximum transmission rate of 10 Mb/s. The length of the balanced twisted pair is inversely proportional to the transmission rate. Below 100 kb/s, it is possible to use the longest specified cable length. The highest rate transmission can only be achieved at a short distance. Generally 100 meters long twisted pair maximum transmission rate is only 1Mb/s.

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