ROC364 Instruction Manual
4-4 Communications Cards Rev Jun/05
4.2.2 EIA-422/485 (RS-422/485) Serial Communications Card
The EIA-422/485 (RS-422/485) communication cards meet all EIA-422/485 (RS-422/485) specifications
for differential, asynchronous transmission of data over distances of up to 1220 meters (4000 feet). The
EIA-422 (RS-422) drivers are designed for party-line applications where one driver is connected to, and
transmits on, a bus with up to ten receivers. The EIA-485 (RS-485) drivers are designed for true multi-
point applications with up to 32 drivers and 32 receivers on a single bus. Refer to Figure 4-2.
NOTE: EIA-422 (RS-422) devices cannot be used in a true multi-point application where
multiple drivers and receivers are connected to a single bus and any one of them can transmit or
receive data.
Figure 4-2. EIA-422/485 (RS-422/485) Serial Communications Card
The current EIA-422/485 (RS-422/485) communications card includes LED indicators that display the
status of the RXD, TXD, and RTS control lines. LED indicators are detailed in Table 4-1. Jumper P4
applies to the transmit mode. The default setting (RTS jumper on) allows a multi-drop configuration, such
as is normally possible with EIA-485 (RS-485) communications. Refer to Section 4.4.2, EIA-422/485
(RS-422 / 485) Communications Card Wiring, on page 4-14 for more information.
LED Indicators
P4 Jumper
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