Comtech EF Data RSU-503 - Manual (Page 51)

Maintenance RSU-503 Redundancy Switch Unit
4–6 Rev. 8
4.5.1 Serial Interfaces (J19, J20, J21)
The internal Serial Interface connectors are 9-pin D with the following pinouts:
Pin # Name Function
RS-232 RS-485
1 GND
2 TD/TX Transmit Data
3 RD/RX Receive Data
4 +RX/TX
5 GND
6 DSR Data Set Ready (Tied high) (see Note 1)
7 RTS -RX/TX Ready to Send (see Note 2)
8 CTS Clear to Send (see Note 2)
9 -RX/TX
Notes:
1. J19 and J20 do not use DSR on pin 6.
2. Clear to Send (CTS) is tied to Ready to Send (RTS) in RS-232 mode.