National Instruments PCI-6281, Руководство пользователя

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B-7
M Series User Manual
Convert Clock
Convert Clock is the signal that determines when an analog to digital conversion is started. The
signal going to the ADC is called p_AI_Convert. Convert Clock also can be routed to several
external I/O terminals for external use. Convert Clock is always generated from the Convert
Clock Timebase signal, either directly or indirectly (by dividing it down using the SI2 counter).
If the SI2 counter is used, it is assumed that a reliable free-running clock is being used. Refer to
the
AI Timing Clocks
section for the timing relationship between Convert Clock Timebase and
Sync Convert Clock Timebase. If the SI2 counter is not being used (external convert case), the
Convert Clock Timebase is assumed to be not free-running and the relationship between the
Convert Clock Timebase and the Sync Convert Clock Timebase is an asynchronous delay.
Whether the SI2 counter is used or not, the timing parameters in the generation of Convert Clock
are the same starting at the Convert Clock Timebase signal.
Table B-2.
AI Timing Clocks Timing
Time Description Line Min (ns) Max (ns)
t
2
Minimum Pulse Width — 12.5 —
t
3
Minimum Period — 50.0 —
t
4
Delay to Sample Clock
Timebase PFI 3.8 9.3
RTSI 3.5 9.0
STAR 3.0 6.4
t
5
Delay to Sync Sample Clock
Timebase PFI 3.4 8.5
RTSI 3.2 8.3
STAR 2.7 5.6
t
6
Delay to Convert Clock
Timebase PFI 4.1 10.2
RTSI 3.9 9.9
STAR 3.4 7.3
t
7
Delay to Sync Convert
Clock Timebase PFI 3.6 8.9
RTSI 3.3 8.6
STAR 2.9 6.0