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5−
25
5. 54550 sends the current SSM status to the terminal interface. (For the
54523, it is Stratum 2.)
If the active clock card receives an SSM that is lower than its own stratum
level, it will treat the case as LOS.
If there is no SSM in the DS1 input, the clock will send out STU (SSM
unknown), e.g. ESF with no code word or SF.
If one input DS1 has a higher level of sync status, the clock card will
automatically switch to input the higher level DS1.
During input tracking, if the input SSM changes, the clock card will change its
output SSM accordingly within 5 seconds.
Before the clock card is stabilized, such as in the Free Run or Acquire 1 state,
the active clock will output a DUS ("Do not use") SSM. This is during initial
startup. After the startup period, the SSM described above will be generated
or passed through.
If a command is executed for SSM on the standby clock card, the SSM
message will be STU. In this case the message should be ignored.
5.6224 Power
An on-card power converter provides the necessary circuit voltages from the
diode-combined A and B -48 volt battery supplies. The on-card fuse, if it
blows, lights the red FAIL LED and provides battery to the Fuse Alarm bus
connecting to pin 10 on the backplane terminal strip TB1.
5.7 Clock Operation, 54522 and 54523 Cards
5.7010 The 54522 Stratum 3E/LNC and 54523 Stratum 2/TNC Track and Hold Clock
Cards have similar algorithms that differ only in the constants assigned for:
•
number of samples of the phase (ACQ_OUT)
•
multiplier for the error from start of tracking (DIF_MUL)
•
multiplier for the error between phase accumulations (DEL_DIF)
•
damping factor for loop response (DAMP)
•
long-term averaging factor (LONGAVG)
5.7011 The constants for both clocks are the same except for the phase
accumulation, or number of samples of the phase, which is 128 for the 54522
Stratum 3E/TNC and 32,768 for the 54523 Stratum 2/TNC.
5.7012 The accumulated phase takes about 0.5 seconds to calculate on the Stratum
3E/LNC and 7 to 8 seconds on the Stratum 2/TNC. The accuracy of the
phase calculation of the Stratum 3E/LNC is 1/4 UI or 162 nanoseconds.
Accuracy of the phase calculation on the Stratum 2/TNC is better than 0.04
nanosecond due to a dither circuit that extends the accuracy of the phase
