RS422 Protocol implementation using 8051


Thread Starter


Hi I am sending Data on RS422 using 8051 Microcontroller . Can anybody tell me where can I get Info about RS422 protocol implementation. I want to write assebly program for RS422 Protocol But i could not find deatails of RS422 Protocol...plzzzz Help

Thanking You

RS422 is not a protocol, it is a line interface standard. It describes signal and medium characteristics. You use it to implement a data link. The protocol is the set of rules for exchanging messages between the /boxes/ devices/ computers/ PLCs on each end of the data link.

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Thomas Hergenhahn

RS422 is not a protocol, but a definition of the physical interface, i.e 0 or 1 is represented by differential voltage. You can transmit any protocol over that physical layer. What protocol you need depends on the device you are talking to.
Hi Chinmay,

RS422 is not a protocol; it is a physical link. Do you mean to implement the hardware handshake transmission between RS422 chip with 8051 or the data transmission way (protocol) among equipment? In the first case, you need RS422 chip datasheet (for example SN75176 from Texas Instruments). In the second, you can use Modbus protocol ( "": ). Hope this help.


Hung Lam
RS-422 is not a protocol, it is a wire / signal "Recommended Specification". As such, the message format you use over RS-422 is entirely up to you. And you can easily use any protocol that is typically used on RS-232 on RS-422 as well. The software would not know the difference. The only time it gets at all complex is when you want
to do RS-485, then the software can only operate only in a master<>slave mode (poll, response). Some decent examples of a popular protocols are:
1. Modbus (Ascii or RTU)
2. Allen-Bradley DF1
4. PPP

There are MANY more, the first two are popular in industrial automation.