C.1 Introduction
157
date, time changes and time quality information of the time signal. Timing information is divided
into logic ones, zeros and reference bits.
There are three functional groups of bits in the IRIG-B time code, in the following order: -
Binary Coded Decimal (BCD), Control Function (CF) and Straight Binary Seconds (SBS). The
BCD group contains only time information including the (daily) hours, minutes and seconds and
recycles yearly. The CF group contains year, time quality, leap year, pending leap seconds and
parity. The SBS consists of the total elapsed seconds that recycles daily.
C.1.2
IRIG-B Type Codes
The Model 1133A provides IRIG-B that follows one type code: unmodulated (or demodulated)
IRIG-B. Also, this signal type is further subdivided according to whether the IRIG-B time code
includes the C37.118 extension. The Model 1133A allows you to enable or disable the C37.118
extension (IEEE 1344 mode ON or OFF), the differences depicted in Table C.1.
1344 Mode
1344 ON
1344 OFF
Unmodulated, B00X
B000
B003
Modulated, B12X
B120
B123
Table C.1: IRIG-B Code Designations
C.1.3
IRIG-B C37.118 Extension
As mentioned above, C37.118 enables extra bits of the Control Function (CF) portion of the IRIG-
B time code. Within this portion of the time code, bits are designated for additional features,
including:
◦
Calendar Year (2 digits)
◦
Leap seconds
◦
Daylight savings
◦
Local time offset
◦
Time quality
◦
Parity
◦
Position identifiers
To be able to use these extra bits of information, relays, RTU’s and other equipment receiving
the time code must be able to decode them. Consult your equipment manual to determine if the
1344 mode should be turned ON in the Model 1133A. To view details of the C37.118 standard,
please check with the IEEE.
NOTE
: To obtain a copy of of the IRIG-B 2004 specification, please use the link to the Arbiter
web site,
http://www.arbiter.com
and check under Documentation
>
Timing and Frequency.
