2. Serial communications

Serial communications are regulated by :

• RS 232C/422/423/449 ;

• CCITT V24 (Europe) ;

• 20 mA current loop.

The 20 mA current loop is tending to disappear because of its speed limitations (remember that it was used to ensure communications with teletypes). It remains very useful for long-distance links.

The RS 422 standard is very similar to RS 232C; the difference lies in the transmission lines: in RS 422, the signal is transmitted differentially on two lines isolated from ground (this is not the case with RS 232C). The purpose of this configuration is to increase transmission speed.