Specifications
2-Series RS-232/422/485 Expansion Card Crestron C2COM-3
NOTE: The pinout of each 9-pin port is non-standard. Therefore, do not use a
straight-through DB9 cable. The following table contains pinout descriptions for
RS-232 and RS-422. Conflicts with some equipment may occur unless the controlled
devices are properly wired. Certain devices have specific voltage requirements.
Therefore, do not use all nine pins in a given application. Although the possibility is
remote, improper wiring may result in damage to the controlled device. Only the
required pins for each communication type should be connected.
Non-Standard COM Pinout (for RS-232 and RS-422 Communication)
PIN DIRECTION DESCRIPTION
1* To C2COM-3
(RXD-) RS-422 Receive Data (Idles low)
2 To C2COM-3
(RXD) RS-232 Receive Data
3 From C2COM-3
(TXD) RS-232 Transmit Data
4 From C2COM-3
(TXD+) RS-422 Transmit Data (Idles high)
5 Ground
RS-232 and RS-422 Signal Common
6 To C2COM-3
(RXD+) RS-422 Receive Data (Idles high)
7 From C2COM-3
(RTS) RS-232 Request to Send
8 To C2COM-3
(CTS) RS-232 Clear to Send
9 From C2COM-3
(TXD-) RS-422 Transmit Data (Idles low)
Where: * = 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.
A common application is to use a three-wire null modem serial cable to
communicate with a PC, as shown below. Since the pinout on the C2COM-3 is non-
standard, the card should not be plugged into the PC directly. The pinout in this
illustration emulates the IBM PC AT connector except for the RS-422 signals on
pins 1, 4, 6, and 9.
Three-Wire Null Modem Serial Cable
RED
WHITE
BLACK
RXD 2
TXD 3
GND 5
3 RXD
2 TXD
5 GND
9-PIN FEMALE
"D" CONNECTOR
9-PIN FEMALE
"D" CONNECTOR
NOTE: To support RS-485, tie pin 1 (RXD-) to pin 9 (TXD-) and pin 4 (TXD+) to
pin 6 (RXD+) in the cable (refer to the following table).
COM Pinout to RS-485 Bus
COM (DB9) CONNECTOR RS-485 BUS
Tie Pins 1 & 9 +
Tie Pins 4 & 6 -
Pin 5 G
4 • 2-Series RS-232/422/485 Expansion Card: C2COM-3 Operations & Installation Guide - Doc. 8176