Symmetricom XLi IEEE 1588 User Manual

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beginning of each frame and a position identifier marks the end of every ten elements.  IRIG-B and IRIG-
A have ten position identifiers per frame.

The elements prior to position identifier P5 comprise the time of year segment. The first ten elements 
encode the seconds, the second ten elements encode the minutes and so on through days.  Each 
element is a digit in a binary number with a place value sequence 1 2 4 8.

Five flags are encoded in the control function segment of the IRIG-B code.  The first flag  encoded at 
element P5+40ms is the LOCK indicator.  It is a binary 1 when the XLi is not locked to a reference.  The 
second flag encoded at element P5+60ms is a binary 1 when the worst case time error exceeds 
threshold 1 (refer to "Function 5 -- Time Quality Enable/Setup").  Element P5+70ms is a binary 1 when 
the worst case time error exceeds threshold 2.  Element P5+80ms encodes a binary 1 when the error 
exceeds threshold 3 and P5+90ms when the error exceeds threshold 4. 

The XLi provides the following IRIG time code outputs (refer to IRIG Standard 200-95):

IRIG-B: B120

1 KHz sine wave amplitude modulated with BCD, CF, SBS

B000 

DC level shift, width coded with BCD, CF, SBS

IRIG-A: A133

1 KHz sine wave amplitude modulated with BCD, SBS

A003 

DC level shift, width coded with BCD, SBS

The XLi can also synchronize and lock to IRIG-B and IRIG-A input codes. The required input code does 
not need to have the CF or SBS elements. The XLi only decodes the BCD portion of the incoming code.

IRIG-B: B122

1 kHz sine wave amplitude modulated with BCD

B002 DC level shift, width coded with BCD

IRIG-A: A132

10 kHz sine wave amplitude modulated with BCD, SBS

A002 DC level shift, width coded with BCD, SBS

The NASA 36 time code is similar to the previously mentioned IRIG codes. The NASA 36 code frame 
also contains 100 bit elements like the IRIG codes. In the strict sense, NASA 36 encodes Universal