Specifications

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)
2To 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 hi
g
h
)
5
RS-232 and RS-422 Si
g
nal Common
6To ST-COM
(
RXD+
)
RS-422 Receive Data
(
Idles hi
g
h
)
7 From ST-COM
(
RTS
)
RS-232 Re
q
uest to Send
8To 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