ML0044B December 1, 2017 - 49 - Copyright 2017 Bitronics, LLC
3.7 Optional IRIG-B Port
The IRIG-B option allows PPX II system time to be regulated by an IRIG-B clock
source. If the clock source is synchronized by GPS, PPX II system time can be aligned
with other devices with great precision.
Unmodulated IRIG-B input allows system time regulation to 1us, IRIG-B 1kHz
modulated input allows system time regulation to 1ms.
PPX II IRIG-B input decodes a signal as defined in the IRIG Standard 200-04, with
support for IEEE 1344 extensions. C37.118-1-2011 elements are parsed, but are
currently unused.
IRIGB has 10Ms bit rate, 100 bits per frame, with 1 frame per second.
IRIGB has a 3 digit suffix. The suffixes supported by PPX II are:
Modulation
0 DCLS (Direct Current Level Shift) - allows 1us regulation
1 Sine wave carrier - allows 1ms regulation
Carrier frequency
0 no carrier (DCLS)
2 1kHz carrier
Coded Expressions
0 BCD, CF, SBS
1 BCD, CF
2 BCD
3 BCD, SBS
4 BDC, BCD_Year, CF, SBS
5 BCD, BCD_Year, CF
6 BCD, BCD_Year
7 BCD, BCD_Year, SBS
PPX II supports the following IRIG-B formats:
B000 thru B007 and B120 thru B127
PPX II automatically detects demodulated (DCLS) and modulated input, switching as
appropriate. Modulated input is indicated by the 'IRIG-B MOD' led on the front panel.
Any absent or malformed input frame causes the IRIG-B to flag the IRIG-B input as
invalid. One complete valid frame must be decoded before declaring IRIG-B input
valid.
If the IRIGB input frame contains century data, it is used, otherwise the system time
year is used (initially obtained at boot from the RTC chip).
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