5.4. Example Program
Glossary
The following is a glossary of key terms used in the discussion of timing operations: An expanded
glossary of terms is available on-line at:
http://www.symmetricom.com/resource/glossary/
BCD: Binary Coded Decimal. Also called packed decimal, this is the representation of each digit of a
decimal number by four-bit binary numbers. For example, the number 42 would be encoded as 0100
0010 .
Coordinated Universal Time (UTC): See UTC.
COTS: Commercial Off-The-Shelf products or services that are generally available and not built to
customized specifications.
DCLS: Direct Current Level Shift, or digital IRIG.
Discipline: The word discipline, as used in this manual, means to adjust the frequency of the 10 MHz
oscillator to track the incoming reference signal.
DPRAM: Dual Port RAM.
Epoch: A reference time or event. Epoch often refers to a one pulse per second event.
Event: An event is defined here as a transition of a digital signal (rising or falling), which can be used
to time stamp the event.
Flywheel: To maintain time or frequency accuracy when the reference source has been lost or
removed.
GPS: Global Positioning System. Originally designated NAVSTAR (Navigation System with Timing
And Ranging), GPS was developed by the US Department of Defense to provide all-weather round-
the-clock navigation capabilities for military ground, sea, and air forces.
HW: Hardware.
IRIG: Serial time format standard maintained by the Inter Range Instrumentation Group.
ISA: Industry Standard Architecture; desktop PC adapter board specification.
Jamsync: Is the process of abruptly synchronizing with a time reference, as opposed to gradually
adjusting to match up with the time reference.
Major Time: Units of time larger than or equal to seconds.
MHz: A MegaHertz is one million (1,000,000) cycles per second.
Minor Time: Sub-second time to whatever resolution is supported.
MTBF: Mean Time Between Failure, a measure of reliability. The longer the time span between fail-
ures, the more reliable the device.
MTTR: Mean Time To Repair.
NASA 36: National Aeronautics & Space Administration 1-second BCD 36-bit Time Code.
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