31
MULTIPORT CSU/DSU
NOTE
Pinout requirements for null-modem applications vary widely between
manufacturers. If you have any questions about a specific application,
call Black Box Technical Support at 724-746-5500.
4.1.4 C
ONFIGURING THE
X.21 M
ODULE
The serial port on the X.21 interface module is default wired as a DCE, but may be
switched to a DTE. Simply reverse the orientation of the DCE/DTE strap, as
described below.
To reverse DCE/DTE orientation, remove the module according to the
instructions in
Section 4.1.1
. The DCE/DTE strap is located on the bottom side of
the module’s PC board. The arrows on the top of the strap indicate the
configuration of the X.21 port (for example, if the DCE arrows are pointing
toward the DB15 connector, the X.21 port is wired as a DCE). Reverse the
DCE/DTE orientation by pulling the strap out of its socket, rotating it 180°, then
plugging the strap back into the socket. You will see that the DCE/DTE arrows now
point in the opposite directions, showing the new configuration of the X.21 port.
Re-install the module according to the instructions in
Section 4.1.1
.
4.2 Connecting the Twisted-Pair Interface
The network interface is an 8-position modular connector. Connect this port to the
RJ-48 female jack provided by the digital data service provider. If you’re using the
CSU/DSU for private short-haul communication, the twisted-pair cable will
connect to this port. See
Appendix A
for the pin assignments of this connector.
The RJ-48 female connector on the CSU/DSU’s twisted-pair interface is pre-
wired for a standard telco wiring environment. The signal/pin relationships are
shown in
Figure 4-2
.
Figure 4-2. CSU/DSU’s Twisted-Pair Line Interface.
1
2
3
4
5
6
7
8
1 (TX+)
2 (TX-)
3 (N/C)
4 (N/C)
5 (N/C)
6 (N/C)
7 (RX+)
8 (RX-)
