8.2 EIA485 Field Communications Port

 

To use EIA485, buffer the EIA232 port of the PC with a suitable EIA232/EIA485 converter. The KD485 Communications Adapter unit is recommended for this purpose. The use of a EIA485 board built into the computer is not recommended since this board may not be isolated, which may cause noise problems, and the RX terminals may not be biased correctly for this application.

 

To construct a cable for EIA485 operation use a screened cable with one (EIA485) twisted pair plus a separate core for common. Although common or screen connections are not necessary, their use will significantly improve noise immunity.

 

See section 2.15 for wiring diagrams.

 

Warning.

The 800 Range has a limited number of writes to EEPROM. Please ensure that parameters which do not require updating on a regular basis (for example, setpoints, alarm trip levels, hysteresis, etc) are only written to when a change in the parameter value occurs. Failure to do this could result in permanent damage to the internal EEPROM.

 

See also section 8.4.