RS-232/422/485 COM Module
Crestron
ST-COM
COM A/B
These two nine-pin connectors (DB9) connect to serial equipment. These
bidirectional serial ports are used for RS-232, RS-422, or RS-485 communication.
NOTE:
The pinout of each nine-pin port is non-standard (refer to table after this
note); it contains RS-422 pins in addition to RS-232. This may result in a conflict
with some equipment and therefore do not use all nine pins. Only the required pins
for each communication type should be connected.
NOTE:
To support RS-485, tie pin 1 (RXD-) to pin 9 (TXD-) and pin 4 (TXD+) to
pin 6 (RXD+) in the cable, as shown below.
ST-COM Pinout (COM A / B)
PIN
DIRECTION
DESCRIPTION
1*
To ST-COM
(RXD-) RS-422 Receive Data (Idles low)
2
To ST-COM
(RXD) RS-232 Received Data
3
From ST-COM
(TXD) RS-232 Transmitted Data
4
From ST-COM
(TXD+) RS-422 Transmit Data (Idles high)
5
RS-232 and RS-422 Signal Common
6
To ST-COM
(RXD+) RS-422 Receive Data (Idles high)
7
From ST-COM
(RTS) RS-232 Request to Send
8
To ST-COM
(CTS) RS-232 Clear to Send
9
From ST-COM
(TXD-) RS-422 Transmit Data (Idles low)
* RS-422 transmit and receive are balanced signals requiring two lines plus a ground in each direction.
RXD+ and TXD+ should idle high (going low at start of data transmission). RXD- and TXD- should idle
low (going high at start of data transmission). If necessary, RXD+/RXD- and TXD+/TXD- may be
swapped to maintain correct signal levels.
4
•
RS-232/422/485 COM Module: ST-COM
Operations Guide - DOC. 5695A
