Symmetricom TM7000, Руководство пользователя

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CHAPTER FOUR
Figure 4.1.1 shows a simplified diagram of a typical Time Code Generator. The significant
sections of a Time Code Generator are:
•
Frequency Source – Usually a crystal controlled oscillator.
•
Minor Time Counters – The purpose of these counters is to develop scan terms and
rates required to develop the Serial Code format or to be used for parallel outputs.
They also supply a 1PPS signal that is used to update the Major Time Accumulator.
•
Major Time Accumulator – This section is a counter whose function is to store the
Time-of-Year data. It is incremented by the 1PPS clock output of the Minor Time. Its
outputs are buffered and used for parallel outputs or are scanned by the Encoder and
output in a serial format.
•
Counter Control – This section synchronizes the time accumulators (Minor Time) and
includes switches to select and enter the Time-of-Day into the Major Time
Accumulator.
•
Parallel-to-Serial Converter – This section consists of scan gates that serialize the
contents of the accumulator into a continuous pulse train.
•
Formatter – This section uses pulse rates from the Minor Time Counter to obtain the
pulse widths and index pulses required to provide the format defined by the type of
time code being generated. This format is then usually combined with a sine wave to
provide an amplitude-modulated signal.
•
Output Amplifier – This section provides the required output drive and signal levels
of the formatter output.
•
Display – This section provides a visual interface between the Generator and the
operator.
1PPS
COUNTER
CONTROL
MINOR
TIME
MAJOR
TIME
DISPLAY
FORMATTER
PARALLEL TO SERIAL
CONVERTER
AMP
FREQUENCY
SOURCE
Figure 4.1.1
Typical Time Code Generator
4-2 TM7000 TymMachine TCG/T (Rev D) Symmetricom, Inc.