The following topics describe the RS-232, RS-422, and RS-485 standards and explain some of the issues involved with these types of serial communication.

RS-232

RS-422

RS-485

Serial Communication Issues

Duplex Architectures

Full Duplex

Half Duplex

RS-485 Termination

Bias Resistors

RS-232 DTE versus DCE

The following table lists the features of the RS-232, RS-422, and RS-485 standards.

RS-232, RS-422, and RS-485 Features

Feature RS-232 RS-422 RS-485
Type of transmission lines Single ended Differential Differential
Maximum number of drivers 1 1 32
Maximum number of receivers 1 10 32
Maximum cable length 50 ft 4,000 ft 4,000 ft
Maximum data rate 20 kbytes/s 10 Mbytes/s 10 Mbytes/s
Maximum CMV ± 25 V ±7 V +12 to –7 V
Driver output 5 to 25 V 2 to 6 V 1.5 to 6 V
Driver load <3 k 100 60