CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 27)

2240 Fiber Optic Modem
27
2.2.5 EXTRA CLOCK Jumper
This two-pin jumper (W26, labeled XTCLK), in conjunction with the enhanced
interfaces (- 422, - 436 and - 430), allows the 2240 to accept BOTH customer clocks
for tail circuit applications. Refer to the RS-449, V.35 and RS-530 interface
sections for more information on the enhanced interfaces. This jumper causes the
2240 to shift data out (RXD) from the 2240 in sync with either the 2240's SCR
(present operation) or the extra clock pins on enhanced interfaces. In the case of the
RS-530 interface there are no unused pins, so a switch on the RS-530 interface is
used to select the direction of the SCT leads (refer to RS-530 interface section). In a
typical application (see Figure 2-5) these extra clock pins would be cabled to the
customer's T1 CSU / DSU's SCT (ST) pins (keep in mind that the 2240s are acting
as a tail circuit). This feature is also necessary if older "gapped clock" CSU / DSUs
are used.
With the jumper OFF, the 2240 shifts data out (RXD) in sync with its SCR signal.
With the jumper ON, the 2240 shifts data out (RXD) in sync with the extra clock
signal.
Factory Setting = OFF
Figure 2-5 illustrates the use of extra clock pins in a tail circuit application at the
clock source end.