Symmetricom XLi IEEE 1588 User Manual

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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.

The level shifted, pulse width modulated, serial format of NASA 36 is divided into two segments.  The 
first segment encodes time of year in binary coded decimal (BCD) notation.  The second segment 
encodes control functions (unused on Model XLi). 

The two code segments are contained within one "frame". The frame length for NASA 36 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 2 ms, a one is 6 ms, a position identifier is 6 ms. A reference marker is 5 consecutive position 
identifiers.  A reference marker locates the beginning of each frame.

The XLi provides the following NASA 36 time code outputs:

NASA 36 (AM):1 KHz sine wave amplitude modulated BCD   

NASA 36 (DC):DC level shift, width coded BCD

The XLi can also synchronize and lock to the following NASA 36 input codes. 

NASA 36 (AM):1 KHz sine wave amplitude modulated BCD   

NASA 36 (DC):DC level shift, width coded BCD