Chapter 4
Connecting the Signals
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National Instruments Corporation
4-33
The ADC switches to hold mode within 60 ns of the selected edge. This
hold-mode delay time is a function of temperature and does not vary from
one conversion to the next. Separate the CONVERT* pulses by at least one
conversion period.
The sample interval counter on the NI 6052E generates CONVERT*
unless you select an external source. The STARTSCAN signal starts the
counter, which counts down and reloads itself until the scan finishes. The
counter then reloads itself in preparation for the next STARTSCAN pulse.
A/D conversions generated by an internal or external CONVERT* signal
are inhibited unless they occur within a sequence. Scans occurring within
a sequence can be gated by either the hardware AIGATE signal or the
software command register gate.
AIGATE Signal
Any PFI pin can externally input the AIGATE signal, which is not
available as an output on the I/O connector. AIGATE can mask off scans
in a sequence. You can configure the PFI pin you select as the source for
AIGATE in level-detection mode. You can configure the polarity selection
for the PFI pin as either active high or active low.
In level-detection mode, the STARTSCAN signal is masked off and no
scans can occur.
AIGATE can neither stop a scan in progress nor continue a previously
gated-off scan. In other words, once a scan has started, AIGATE does not
gate off conversions until the beginning of the next scan. Conversely, if
conversions are gated off, AIGATE does not gate them back on until the
beginning of the next scan.
SISOURCE Signal
Any PFI pin can externally input the SISOURCE signal, which is not
available as an output on the I/O connector. The onboard scan interval (SI)
counter uses SISOURCE as a clock to time the generation of the
STARTSCAN signal. Configure the PFI pin you select as the source for
SISOURCE in level-detection mode. Configure the polarity selection for
the PFI pin for either active high or active low.
The maximum allowed frequency is 20 MHz, with a minimum pulse width
of 23 ns high or low. There is no minimum frequency.
