National Instruments PXI-6683 Series, User Manual, Page: 34 / 66

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Chapter 4 Synchronization
When configured to synchronize to an IRIG-B AM source, the NI PXI-6683 Series will be able
to accept a 1 kHz AM modulated IRIG-B 12X signal on its PFI0 input. When configured to
synchronize to an IRIG-B DC source, the NI PXI-6683 Series will be able to accept an
IRIG-B 00X DC encoded signal on its PFI0 input.
Caution
Do not connect an AM signal to PFI0 when the PFI line is configured for
digital operations. This could cause damage to the digital circuitry, the device driving
the AM signal, or both. Always ensure the line is configured for IRIG-B AM
operation before connecting an IRIG-B AM signal.
Furthermore, once the NI PXI-6683 Series is synchronized to IRIG-B, it can function as an
IEEE 1588 grandmaster to synchronize of external 1588 devices.
The following assumptions are made regarding the received IRIG-B signal. All conditions must
be met for the NI PXI-6683 Series to be able to synchronize accurately:
•
Seconds begin every minute at 0, increment to 59, and then roll over to 0.
• Minutes begin every hour at 0, increment to 59, and then roll over to 0.
• Hours begin every day at 0, increment to 23, and then roll over to 0.
• Days begin every year at 1. Days increment to 365 in non-leap years, or to 366 in leap years,
and then roll-over to 1. Leap years must be supported. Valid values for year are 01 to 99,
inclusive. Years are assumed to be in the XXI Century. For instance, year
09 represents
2009. If the year is not supplied (sent as 00 ), the OS system time is read and the year is
derived from it.
To achieve proper synchronization of the NI PXI-6683 Series, ensure that the IRIG-B source
used conforms to the requirements listed above. Note that most IRIG-B sources conform to these
requirements.
IEEE 1588
The NI PXI-6683 Series is capable of performing synchronization over Ethernet using
IEEE 1588. It is possible to configure the NI PXI-6683 Series to synchronize to GPS or IRIG-B
and then function as an IEEE 1588 grandmaster. It is also possible to configure the NI PXI-6683
Series to synchronize to IEEE 1588, in which case, the standard defines how the master will be
selected. If the NI PXI-6683 Series is selected as IEEE 1588 master, and it is not configured to
synchronize to GPS or IRIG-B, it will use its internal free-running timebase, which will be
updated to the host computer’s system time during power up.