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5−
19
following initial qualification, the clock will be in tracking mode. After 45 to
60 minutes, the tracking mode will be at minimum error if the input is within
specifications. The 54523 will track timing from another Stratum 2/TNC or
Stratum 1/PRC source having an average frequency offset of no more
than ±0.04 Hz. The signal to the output cards is continuous (no phase
hits) during any switch from track to hold. Frequency and phase
corrections occur over periods of about 10,000 seconds. A fast ACQUIRE
state reduces this to 300 seconds for power-up and 1000 seconds for
return from the HOLD state.
c. Accepts an alternate external 5 or 10 MHz signal from a high stability
timing source such as a GPS receiver, cesium clock, or similar
mechanism. This signal may be used as a tracking input. The external 5
or 10 MHz signal is selected as a tracking reference through user
commands to the 54550 Information Management Card.
d. Supplies monitoring and alarm information to the 54550 Information
Management Card and 54560 Alarm Interface Card.
e. Facilitates synchronization status messaging per Bellcore GR-378
(DS1/E1 only).
5.62 Circuit
Description
Refer to the block diagram in Figure 5-5 in the following discussion.
5.6210 Microcontroller
The functions of the 54523 track and hold card are controlled by a DS80C320
microcontroller. The DS80C320 memory space consists of two 64K blocks of
memory, one each for program and data.
5.6211 DS1/E1/2048 KHz/CC/5 MHz/10 MHz Input
The 54523 card gets its input clock from the 54511, 54512, or 54513 Input
Card. It selects either the A or B input reference signal via the backplane
connector.
a. For the AB input architecture, the primary reference for the A track and
hold card is DS1/E1 Input A and for the B track and hold card it is DS1/E1
Input B.
b. For the AA input architecture, the primary reference for both track and hold
cards is DS1/E1 Input A. In this state, the Input A LEDs are illuminated on
both track and hold cards.
Input references can only be changed by commands from a terminal by
means of TL1/ITL1 or the menu screens. This should only be done to
provide temporary backup in the event that one input has failed and cannot
be fixed for an extended period of time. In all normal operating modes, the
track and hold cards should be tracking their corresponding inputs.
Содержание 54500-16
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