ACE1553-3U-4 Hardware Manual
20
4.1.2 System Reference Clock (10MHz)
The PXI backplane has a built-in, dedicated 10 MHz system clock.
This very high quality clock, with low skew signals between each slot, is used for synchronizing
modules. When boards are synchronized in an industrial PC, or any other system for that
matter, they must be cabled together with a proprietary trigger bus and timing sources on the
boards
are
used
to
time
and
trigger
the
boards.
Because the quality and precision of the clock depends on the individual device, some are more
or less precise than the industrial PC chassis clock. However, because the clock signals are
routed among boards, they have a higher skew
– typically nanoseconds versus picoseconds –
than the chassis clock and the signals are not shielded. The PXI system clock is able to
maintain its quality by using a low-skew, fan-out buffer chip that essentially provides a unique
clock for every slot. Furthermore, because the clock lines are built into the backplane, the lines
are better shielded than external lines.
The ACE1553-3U-4 card can be set to deliver the PXI 10 MHz System Clock to its internal
TIME TAG generation circuitry. The IRIG decoder will then work in Free-Wheeling mode
but synchronous to the PXI 10 MHz clock. It is possible to maintain the synchronization
among more AIM PXI-capable cards on the same backplane using the TIME TAG reset
feature (see next paragraph).
Please NOTE:
For electrical specification please refer to reference
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