INTRODUCTION
Symmetricom Inc
bc635VME/bc350VXI Time and Frequency Processor (Rev. E)
1-7
This function group provides access to functions controlling TFP card operation while decoding
time code. These functions allow the user to control both the time code decoding and time code
generating circuits of the device.
1.5.2.1 DECODE
This function allows the user to select the format and modulation types associated with an input
timing signal. These values control how the device attempts to decode the input time code.
These values may be set regardless of the mode but will only be used in time code decoding
mode. The format defines the type of the time code data. The modulation defines the envelope
for the signal and which input pin the signal will be extracted from. The default format is IRIG
B and the default modulation envelope is AM (amplitude modulated).
1.5.2.2 GENERATE
This function allows the user to select the format of the time code that will be generated by the
TFP device. The time code generator supports IRIG B and IRIG H DCLS.
1.5.3 SIGNALS
This group provides access to functions that control various hardware timing signals either
decoded or generated by the TFP card.
1.5.3.1 HEARTBEAT (PERIODIC) OUTPUT
This function allows the user to command the TFP to produce a clock signal at a specified
frequency. The heartbeat signal, also referred to as a periodic, can be either synchronous or
asynchronous to the internal 1PPS epoch in the TFP device. This functionality is implemented
in hardware on the TFP device by an Intel 82C54 counter timer chip. The heartbeat circuit has
two 16 bit divisors, which are clocked by the counter. As the output of the first divisor provides
the clock for the second divisor, manipulating the divisor values results in various duty cycles.
The output of this circuitry is capable of creating a VME bus interrupt. See Section 4.1.5 for a
description of how to program the heartbeat output.
1.5.3.2 STROBE OUTPUT
This function allows the user to command the TFP to produce a hardware signal at a particular
time, or at a particular point during a 1 second interval. When major/minor mode is selected, a
hardware signal will be produced when the internal time of the TFP device matches the values
entered for the major and minor strobe registers. The major time in hours, minutes and seconds
may be supplied in addition to the milliseconds loaded in the minor strobe register. When minor
mode is selected, a strobe signal is produced every second when the internal millisecond count in
the TFP device matches the value entered in the minor strobe register. The output of this
circuitry is capable of creating a VME bus interrupt.
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