Chapter 4
Connecting Signals
4-32
ni.com
Figure 4-25.
WFTRIG Output Signal Timing
UPDATE* Signal
Any PFI pin can externally input the UPDATE* signal, which is available
as an output on the PFI5/UPDATE* pin.
As an input, UPDATE* is configured in the edge-detection mode. You can
select any PFI pin as the source for UPDATE* and configure the polarity
selection for either rising or falling edge. The selected edge of UPDATE*
updates the outputs of the DACs. In order to use UPDATE*, you must set
the DACs to posted-update mode.
As an output, UPDATE* reflects the actual update pulse that is connected
to the DACs, even if the updates are being externally generated by another
PFI. The output is an active low pulse with a pulse width of 300 to 350 ns.
This output is set to high-impedance at startup.
Figures 4-26 and 4-27 show the input and output timing requirements for
UPDATE*.
Figure 4-26.
UPDATE* Input Signal Timing
t
w
= 50 to 100 ns
t
w
Rising-Edge
Polarity
Falling-Edge
Polarity
t
w
= 10 ns minimum
t
w
