Symmetricom XLi IEEE 1588 User Manual

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The following section provides a summary description of the three time code types used by the XLi. 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 

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 XLi. 

The document 200 95 "IRIG STANDARD TIME FORMATS" by the Telecommunications Working Group, 
Inter range Instrumentation Group, Range Commanders Council describes IRIG-B and IRIG-A time 
codes.

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 XLi 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.

Reference 

.  The level shifted, pulse width modulated, serial 

formats of IRIG-B and IRIG-A 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 XLi, this segment 
encodes worst case time error flags as explained below.  The IRIG-A output from Model XLi does not 
include control functions.  The third segment sometimes encodes time of day in straight binary seconds 
(SBS) notation.  Both IRIG-B and IRIG-A encode SBS on the Model XLi.

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.  The frame length 
for IRIG-A is 1/10 seconds and contains 100 elements each of which starts every 1 millisecond.

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