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5.13 Model 54571 T1 Output Driver Card
5.1301
This card provides twenty separate DS1 DSX-compatible framed ones drive
signals, with either SF or ESF framing. The outputs drive any standard T1
receiver through up to 655 feet of cable. An alarm output signal alerts the
54560 Alarm Interface Card when one or more outputs have failed.
5.131 Functions
5.1311
The Model 54571 T1 Output Driver Card provides the following:
a. Clock selection by a logic array based on HOLD indications from the A
and B track and hold cards. The current tracking card or, if both are in
HOLD, the last track and hold card to go into the HOLD state is selected.
Switching is nonrevertive to minimize the number of phase
disturbances.
b. Override lines from the 54550 Information Management Card allowing
for manual clock selection and for automatic switching directly to a
reference input in the event that both track and hold cards fail (Major
alarm state).
c. The first output card from the left (any slot) acting as a master selector
and all other output cards slaved to it, to ensure that all output cards
select the same clock reference.
d. A synchronization bus connecting all output cards to ensure that all
outputs from the shelf are frame and multiframe synchronized for DS1
SF (12 frame multiframe), DS1 ESF (24 frame multiframe), and E1 (16
frame multiframe) outputs.
e. One-wire interface to 54550 Information Management Card for reporting
personality, switch setting, LEDs, and alarms.
f. On-card switch selection of SF or ESF framing.
g. On-card jumper selection of Protected or Non-Protected operation.
5.132 Circuit
Description
The 54571 block diagram appears in Figure 5-12.
5.1321
Clock Select Switch
The clock select switch is a 1.544 MHz clock selector with phase buildout
circuit, frame/byte synchronization system, LED indicators, and output
alarms. The selector output goes to a phase buildout circuit whose function
is to smooth out sudden phase changes (which might be as much as ±1/2 a
unit interval) occurring when the clock selection is changed. The change of
phase rate is limited to under 20 nanoseconds (1/32 unit interval) in 14
milliseconds (21,616 unit intervals).
