Chapter 4
Connecting Signals
©
National Instruments Corporation
4-25
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 4-11
and 4-12 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 the starts are being externally triggered by another PFI. You
have two output options. The first is an active high pulse with a pulse width
of 50 to 100 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 4-17 and 4-18 show the input and output timing requirements for
the STARTSCAN signal.
Figure 4-17.
STARTSCAN Input Signal Timing
Rising-Edge
Polarity
Falling-Edge
Polarity
t
w
= 10 ns minimum
t
w
