Appendix B
IRIG Protocol Overview
NI PXI-6682 Series User Manual
B-2
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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.
For example, IRIG-B 120 indicates that the information is sent once per
second, 100 bits per second, on a 1kHz amplitude modulated sine wave,
and that the information sent is the time of year in BCD, control bits, and
the seconds of day in straight binary seconds.
There are 3 types of “bits” sent in the IRIG standard: binary zeroes, binary
ones and position identifiers. To transmit a binary zero, the source must
keep the signal at mark for 20% of the bit duration and at space for the
remaining 80%; to transmit a binary one the source must keep the signal at
mark for 50% of the bit duration and at space for the remaining 50%; to
transmit a position identifier, the source must keep the signal at mark for
80% of the bit duration, and at space for the remaining 20%. Binary bits are
used to transmit information such as time of year, straight binary seconds,
and so on, and position identifiers are used to separate the different
pieces of data transmitted. The second’s boundary is embedded into the
transmission by sending two consecutive position identifiers; the beginning
of the second position identifier is the second’s boundary.
Table B-2.
IRIG Option Characteristics
Modulation
type
Carrier Signal
Frequency
Information sent
0
Pulse width modulated
0
DC
0
TOY (BCD), CB, SBS
1
Amplitude modulated
(sine wave)
1
100 Hz
1
TOY (BCD), CB
2
Manchester modulated
2
1 kHz
2
TOY (BCD)
3
10 kHz
3
TOY (BCD), SBS
4
100 kHz
4
TOY (BCD), Year (BCD),
CB, SBS
5
1 MHz
5
TOY (BCD), Year (BCD), CB
6
TOY (BCD), Year (BCD)
7
TOY (BCD), Year (BCD),
SBS
CB = control bits
