National Instruments NI PCI-6110 - Manual (Page 56)

Chapter 4 Connecting Signals
NI PCI-6110/6111 User Manual 4-26 ni.com
SISOURCE Signal
Any PFI pin can receive as an input the SISOURCE signal, which is not
available as an output on the I/O connector. The SI2 uses SISOURCE as
a clock to time the generation of the STARTSCAN signal. You must
configure the PFI pin you select as the source for SISOURCE in the
level-detection mode. You can 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 limitation.
Either the 20 MHz or 100 kHz internal timebase generates SISOURCE
unless you select some external source. Figure 4-19 shows the timing
requirements for SISOURCE.
Figure 4-19. SISOURCE Signal Timing
SCANCLK Signal
SCANCLK is an output-only signal that generates a pulse with the leading
edge occurring approximately 50 to 100 ns after an A/D conversion begins.
The polarity of this output is software-selectable, but it is typically
configured so that a low-to-high leading edge can clock external AI
multiplexers indicating when the input signal has been sampled and can be
removed. This signal has a 450 ns pulse width and is software enabled.
Note SCANCLK polarity is low-to-high and cannot be changed programmatically using
NI-DAQ.
t
w
= 23 ns minimum
t
p
= 50 ns minimum
t
p
t
w
t
w