Cable Wiring For Serial Port In Regular Rs-422 Mode - 3Com CS/2500 Installation Manual

RS-422 Operation
Table A-1 RS-232 Serial Port Pin Assignments (continued)
RS-232- 3Com
Pin D Name Name
(continued)
21 — —
22 † — RI
*
23 — DTE
RXC
24 * — DTE
TXC
25 ‡ — —
* Pins 11, 23, and 24 are supported on ports J0 and J1 only for synchronous modem support.
† Ring is active when server is on.
‡ Pin 25 is unused in RS-232 operation. If "Automatic RS-422 Port Selection" is enabled, port
switches automatically to RS-422 when active pin 25 is detected.
When an RS-232 serial port is configured for RS-422 operation, only
certain pins are active. When a single port is configured in firmware for
RS-422, pins 13, 14, 16, and 19 are reserved for RS-422 operation.
When all ports are configured for automatic RS-422 port selection, pin
25 is also used as a switch to detect RS-422 operation. Figure A-2 shows
cable wiring for a port configured for normal RS-422 mode. Figure A-3
shows cable wiring when all ports are configured for automatic RS-422
port selection.
DCE
CS/2500 Pin
TXD+
13
TXD-
14
RXD-
16
RXD+
19
Figure A-2 Cable Wiring for Serial Port in Regular RS-422 Mode
RS-232 Serial Ports
Failsafe
Direction State
— —
Out —
In —
In —
— RS-232
A-3
Function
Not used
Ring Indicator
DTE Receive Clock
DTE Transmit Clock
Switch between RS-232
and RS-422 operation