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5−
23
the dominant factor in determining initial behavior.
The control loop of the 54523 is piece-wise linear, since normal and ACQUIRE
2 can alternate.
5.6216 Controls and Latches
The output phase is compared with the phase of the recovered input reference
clock by means of a pair of counters and latches, good signal or bad:
a. When the input signal is deemed good, the microcontroller tracks the input
phase and, every 7 seconds, calculates a new 48-bit control word for the
DDFS based on the input/output phase difference and rate of change. The
16 MSBs of the control word are fixed and the microcontroller calculates
the 32 LSBs.
b. When all inputs are deemed bad, tracking ceases (HOLD mode). Any fault
which triggers the HOLD state saves the last known good output frequency
correction factor and uses it to determine the HOLD frequency.
5.6217 Controls and Indicators
The following controls and indicators appear on the front panel of the 54523
card:
a. The red FAIL LED indicates an internal FUSE has blown, the power supply
is not working, or the processor is not running.
b. The green INPUT A/B LEDs indicate which of the two INPUT signals the
card is tracking.
c. The yellow HOLD LED indicates that the unit is in the HOLD mode.
d. The green ACQUIRE LED indicates that the unit is in the ACQUIRE mode.
e. The green LOCKED LED indicates that the unit is in the LOCKED mode.
f. The yellow FREERUN LED indicates that the unit is in the FREERUN
mode.
g. The green ACTIVE LED indicates that this unit is driving the clock bus.
h. The seven segment display indicates the STATUS of the input failure.
i. The HOLD TEST pushbutton causes the microcontroller to execute a
diagnostic routine and display 'H' if successful. The unit returns to normal
tracking in a few seconds. (An internal TEST/RUN toggle, S2, is set in the
RUN mode for normal operation.) Selecting S2 to be TEST is not
recommended for normal operation.
5.6218 Alarm
Output
The HOLD mode or FAIL condition, or a fault reported by the rubidium
