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B
IRIG Protocol Overview
IRIG (Inter Range Instrumentation Group) is a standard used to transmit precise timing
information between instruments to achieve synchronization. There are 6 different IRIG
standards defined (A,B,D,E,G and H). The main difference between the standards is the rate with
which the synchronization pulses and the information bits are sent. The standards also differ
slightly in the content of the information transmitted. Table B-1 summarizes the characteristics
of each IRIG standard
In addition to the characteristics of each standard described in the table above, each of those is
subdivided further depending on the electrical characteristics of the signal used to transmit the
data, and the actual data transmitted. This is usually specified by 3 digits that follow the IRIG
standard name (for instance, IRIG-B 120). Table B-2 details the different characteristics of each
IRIG option.
Table B-1. IRIG Standard Definitions
IRIG Standard
Bit rate
(bit duration)
Frame rate
(frame duration)
Information sent
IRIG-A 1 Kbps (1 ms) 10 fps (100 ms) TOY & Y (BCD)
SOD (SBS)
IRIG-B 100 bps (10 ms) 1 fps (1 s) TOY & Y (BCD)
SOD (SBS)
IRIG-D 1 bpm (60 s) 1 fph (1 hour) TOY (BCD)
days and hours only
IRIG-E 10 bps (100 ms) 6 fpm (10s ) TOY & Y (BCD)
IRIG-G 10 kbps (0.1 ms) 100 fps (10 ms) TOY & Y (BCD)
Includes fractions of
seconds
IRIG-H 1 bps (1 s) 1 fpm (60 s) TOY (BCD)
Days, hours and
minutes only
bpm—bits per minute
bps—bits per second
fph—frames per hour
fpm—frames per minute
fps—frames per second
BCD—binary-coded decimal
SBS—straight binary seconds
SOD—seconds of day
TOY—time of year
Y—year
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