Chapter 4
Connecting the Signals
4-38
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UISOURCE Signal
Any PFI pin can externally input the UISOURCE signal, which is not
available as an output on the I/O connector.
The UI counter uses UISOURCE as a clock to time the generation of the
UPDATE* signal. You must configure the PFI pin you select as the source
for UISOURCE 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.
Either the 20 MHz or 100 kHz internal timebase normally generates
UISOURCE unless you select an external source.
Figure 4-32 shows the timing requirements for UISOURCE.
Figure 4-32.
UISOURCE Signal Timing
General-Purpose Timing Signal Connections
The general-purpose timing signals are as follows:
•
•
•
•
•
•
•
•
•
t
p
= 50 ns minimum
t
w
= 23 ns minimum
t
w
t
w
t
p
