Chapter 4 Signal Connections
DAQCard E Series User Manual 4-24
National Instruments Corporation
Programmable Function Input Connections There are a total of 13 internal timing signals that you can externally
control from the PFI pins. The source for each of these signals is
software selectable from any of the PFIs when you want external
control. This flexible routing scheme reduces the need to change the
physical wiring to the DAQCard I/O connector for different
applications requiring alternative wiring.
You can individually enable each of the PFI pins to output a specific
internal timing signal. For example, if you need the CONVERT* signal
as an output on the I/O connector, software can turn on the output
driver for the PFI2/CONVERT* pin. Be careful not to drive a PFI
signal externally when it is configured as an output.
As an input, you can individually configure each PFI for edge or level
detection and for polarity selection, as well. You can use the polarity
selection for any of the 13 timing signals, but the edge or level
detection will depend upon the particular timing signal being
controlled. The detection requirements for each timing signal are listed
within the section that discusses that individual signal.
In edge-detection mode, the minimum pulse width required is 10 ns.
This applies for both rising-edge and falling-edge polarity settings.
There is no maximum pulse-width requirement in edge-detection
mode.
In level-detection mode, there are no minimum or maximum
pulse-width requirements imposed by the PFIs themselves, but there
may be limits imposed by the particular timing signal being controlled.
These requirements are listed later in this chapter.
Data Acquisition Timing Connections The data acquisition timing signals are SCANCLK, EXTSTROBE*,
TRIG1, TRIG2, STARTSCAN, CONVERT*, AIGATE, and
SISOURCE.
Posttriggered data acquisition allows you to view only data that is
acquired after a trigger event is received. A typical posttriggered data
acquisition sequence is shown in Figure 4-10. Pretriggered data
acquisition allows you to view data that is acquired before the trigger
of interest in addition to data acquired after the trigger. Figure 4-11