Computer Busses

14

RS-422, RS-423 and RS-485

14.1 Introduction

The main standards organisations for data communications are the ITU (International Telecommunications Union), the EIA (Electronic Industry Association) and the ISO (International Standards Organisation). The ITU standards related to serial communications are defined in the V-series specifications and EIA standards as the RS-series. The EIA has defined many standards for serial communications. RS-232 has many limitations, such as:

• One transmitter and one receiver.

• Maximum connection length of 20m.

• Maximum baud rate of 20 kbps.

The RS-422 and RS-423 standards replace the RS-232 standards and support higher data rates and greater immunity to electrical interference. The main standards are:

• RS-422A ...