14 MDS SD4 Startup Guide 05-4669A01, Rev. A
Pin Descriptions—RS/EIA-422/485 Mode
Table 6 lists the COM connector pin functions for radios configured to
operate in RS/EIA-422/485 mode. See Figure 11 for wiring schemes.
NOTES:
• RXD+ / RXA and RXD– / RXB are data sent into the radio to be transmitted out
• RXD+ / RXA is positive with respect to RXD– / RXB when the line input is a “0”
• TXD+ / TXA and TXD– / TXB are data received by the radio and sent to the connected
device
• TXD+ / TXA is positive with respect to the TXD– / TXB when the line output is a “0”
5 -- Signal Ground—
Connects to ground (negative supply potential) on chassis.
6 OUT Alarm Output (DSR)—An RS-232 high/space (+5.0 Vdc) on
this pin indicates an alarm condition. An RS-232 low/mark
(–5.0 Vdc) indicates normal operation. This pin may be used
as an alarm output. (See Reference Manual.)
7 IN RTS (Request-to-Send)
8 OUT CTS (Clear-to-Send)—Goes “high” after the programmed
CTS delay time has elapsed (DCE), or keys an attached radio when RF data arrives (CTS KEY).
9 -- Not Used—Do not connect
Table 6. COM2 Connector Pin Descriptions—RS/EIA-485 Mode
Pin
Number
Input/
Output Pin Description
1 — Not Used—Do not connect
2 OUT TXD+/TXA—Non-inverting driver output. Supplies data to
the connected device.
3 IN RXD+/RXA—Non-inverting receiver input. Accepts data
from the connected device.
4 -- Not Used—Do not connect
5 -- Signal Ground—Connects to ground (negative supply po-
tential) on the radio’s PC board and chassis.
6 -- Not Used—Do not connect
7 IN RXD– /RXB—Inverting receiving input
8 OUT TXD– /TXB—Inverting driver output.
9 -- Open (User configurable via internal jumper. See Reference
Manual for details.)
Table 5. COM2 Pin Descriptions—RS/EIA-232 (Cont’d)
Pin
Number
Input/
Output Pin Description