Symmetricom XL-GPS - Manual (Page 148)

138 997-01530-01, Rev. C-25, Jan 2008
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E: Time Code Formats
The following section provides a summary description of the three time code types used by the XL-GPS.
The definitive IRIG time code specification, the Range Commanders Council’s IRIG Serial Time Code
Formats, IRIG Standard 200-98, is available on the Web at
http://jcs.mil/RCC/manuals/200/
Overview
Please refer to the Input and Output specifications in the front of the manual for details regarding the
voltage amplitudes / modulation ratios of the following time codes provided or used by the Model XL-
GPS.
IRIG
Introduction
The document 200 95 "IRIG STANDARD TIME FORMATS" by the Telecommunications Working Group,
Inter range Instrumentation Group, Range Commanders Council describes IRIG-B time code.
The standard time formats of IRIG codes were designed for use in missile, satellite and space research
programs. Use of these codes facilitates efficient interchange of test data. These formats are suitable
for recording on magnetic tape, oscillographs, film and for real time transmission in both automatic and
manual data reduction. IRIG-B from the Model XL-GPS is suitable for remote display driving, magnetic
tape recording and many other uses. IRIG codes, in the strict sense, encode Universal Coordinated
Time (UTC) in 24 hour format and not local time. Nonetheless, this instrument can encode UTC or local
time in either 24 or 12 hour formats.
IRIG Code Format
Reference “IRIG Standard Format A” on page 140 . The level shifted, pulse width modulated, serial
formats of IRIG-B are divided into three segments. The first segment encodes time of year in binary
coded decimal (BCD) notation. The second segment encodes control functions. This segment is
generally available for data of the user's choice. In the IRIG-B code output of Model XL-GPS, this
segment encodes worst case time error flags as explained below. The third segment sometimes
encodes time of day in straight binary seconds (SBS) notation. Both IRIG-B encodes SBS on the Model
XL-GPS.
The three code segments are contained within one "frame". The frame length for IRIG-B is 1 second
long and contains 100 "elements" (pulses) each of which start every 10 milliseconds.
An element may represent either a binary zero, a binary one, a reference marker or a position identifier.
A zero is 0.2 of the duration of an element, a one is 0.5 of the duration of an element and a position
identifier or reference marker is 0.8 of the duration of an element. A reference marker locates the