3Com PathBuilder S21x, Installation Manual

Page: 54 / 66

B-12 PathBuilder S21x Switch Cabling
V.24 Cable
V.24 Cable
V.24 DCE Cable
The following table shows the DCE pinouts for the V.24 cable. These pins are
assigned double functions in the V.24 cable:
• Pin 15: Outputs TRANSMIT CLOCK if the port is configured for internal
clocks. Otherwise it acts as a V.54 Loop 3 signal when connected to a modem.
• Pin 22: Used as the Ring Indicator output if the port is configured to emulate a
dial modem. For this to work properly, the RI/TM switch of the port must be
set to RI. When the RI/TM switch is set to TM, this pin acts as an input, and
the TM output from the attached modem (pin 25 on the modem) comes into
the 6500 on this pin.
Pin Function/Signal Name
1 Shield/Frame Ground
2 TXD
3 RXD
4 RTS
5 CTS
6 DSR
7 Signal Ground
8 DCD
14 DATA RESTRAINT
15 TRANSMIT CLOCK or V.54 Loop 3 *
16 STANDBY INDICATOR
17 RECEIVE CLOCK
18 EXTERNAL RECEIVE CLOCK
20 DTR
21 V.54 Loop 2
22 RI/TM *
24 EXTERNAL TRANSMIT CLOCK
25 TEST MODE