Chapter 4
Connecting Signals
4-24
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STARTSCAN Signal
Any PFI pin can receive as an input the STARTSCAN signal, which is
available as an output on the PFI7/STARTSCAN pin. Refer to Figures 4-18
and 4-19 for the relationship of STARTSCAN to the DAQ sequence.
As an input, STARTSCAN is configured in the edge-detection mode. You
can select any PFI pin as the source for STARTSCAN and configure the
polarity selection for either rising or falling edge. The selected edge of
STARTSCAN initiates a scan. The sample interval counter starts if you
select internally triggered CONVERT*.
As an output, STARTSCAN reflects the actual start pulse that initiates a
scan even if another PFI is externally triggering the starts. You have two
output options. The first is an active high pulse with a pulse width of 25 to
50 ns, which indicates the start of the scan. The second action is an active
high pulse that terminates at the start of the last conversion in the scan,
which indicates a scan in progress. STARTSCAN is deasserted t
off
after the
last conversion in the scan is initiated. This output is set to high-impedance
at startup.
Figures 4-18 and 4-19 show the timing requirements for STARTSCAN.
Figure 4-18.
STARTSCAN Input Signal Timing
Rising-Edge
Polarity
Falling-Edge
Polarity
t
w
= 10 ns minimum
t
w
