Symmetricom Inc
bc620/627AT Time and Frequency Processor
3-1
CHAPTER THREE
SOFTWARE INTERFACE
3.0 GENERAL
The bc620/627AT Time and Frequency Processor (TFP) occupies 16 bytes in the PC bus I/O
address space. Refer to Chapter Two for details on base address selection. All TFP registers are
eight bits wide. This chapter describes the TFP registers and their use.
3.0.1 GLOSSARY OF KEY TERMS
Epoch
A reference time or event. In timing applications “epoch” often refers to a one pulse per second
event (1pps).
Flywheel
In the time keeping vernacular, to “flywheel” means to maintain time or frequency or both after
the input reference is removed or lost.
Periodic
A programmable frequency which is obtained by dividing the TFP reference frequency.
Periodics are sometimes referred to as “heartbeats.” Periodics may optionally be synchronous
with the 1pps epoch if the period is expressible as a ratio of integers.
Major Time
Units of time larger than or equal to seconds. A day hr:min:sec format is usually implied.
Minor Time
Subsecond time to whatever resolution is supported.
Packet
A group of bytes conforming to a defined structure. Packets are usually used in bit serial or byte
serial data transmission to allow framing of the transmitted data.
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