17
MULTIPORT CSU/DSU
Switches S2-4 and S2-5: Clock Mode
Use Switches S2-4 and S2-5 to set the source of the CSU/DSU’s transmit clock.
Table 3-10. Settings for Switches S2-4 and S2-5.
S2-4
S2-5
Clock Mode
Description
On
Off
External (DTE)
Transmit clock derived from terminal
interface.
Off
Off
Network (Looped)
Transmit clock derived from the
received line signal; use this mode for
dedicated DDS operation.
On
On
Internal (Master)
Transmit clock derived internally.
Off
On
Campus Clock
Transmit clock derived from the
received line signal. Allows remote
device (in campus clock mode) to
initiate V.54 loopback. For use only in
campus short-haul configuration.
(NOTE: Local device must be set in
internal
clock mode.)
NOTE
For X.21 or async campus short-haul modem applications, configure
one Multiport CSU/DSU for internal clock mode and the other CSU/DSU
for receive recover clock mode.
Switch S2-6: Force RTS
Use S2-6 to force the transmitter On, thereby ignoring the DTE’s RTS signal. In
the Off position, RTS controls the transmitter by forcing it to send either the DTE
data or an idle pattern.
Table 3-11. Settings for Switch S2-6.
S2-6
RTS
Description
On
Forced On
Transmitter is always ON
Off
Follows DTE signal
The RTS input controls the transmitter
