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5−
29
5.82 Circuit
Description
Refer to the block diagram in Figure 5-7 during the following discussion.
5.8210 Microcontroller
The functions of the 54591 track and hold card are controlled by an 80C320
microcontroller. The 80C320 memory space consists of two 64K blocks of
memory, one each for program and data.
5.8220 Inputs
a.
GPS
Receiver
The 54591 card supplies the GPS receiver with the 1.544 MHz reference. The
receiver determines the error in the 1.544 MHz with respect to the GPS signal. The
microcontroller reads the error from the GPS receiver and provides a correction to the
DDFS setting.
b.
DS1/E1
Input
The 54591 card gets its clock from the 54511 or 54512 Input Card. It selects either
the A or B input reference DS1/E1 signal via the backplane connector.
The 54591 is provisioned at the factory with AB input architecture.
1. Assuming that there are acceptable T1/E1 signals at Inputs A and B, 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.
2. The 54591 can select Input B to be from Input Card A by activating the
CLKSEL output line.
Input references can only be changed by commands from a terminal as described in
the StarClock 200E User Manual, Volume 3 (TL1/ITL1) or Volume 4 (Menu).
