National Instruments E Series - Manual (Page 36)

Chapter 3 Hardware Overview
DAQCard E Series User Manual 3-14  National Instruments Corporation
Programmable Function Inputs
The 10 PFIs are connected to the signal routing multiplexer for each
timing signal, and software can select one of the PFIs as the external
source for a given timing signal. It is important to note that any of the
PFIs can be used as an input by any of the timing signals and that
multiple timing signals can use the same PFI simultaneously. This
flexible routing scheme reduces the need to change physical
connections to the I/O connector for different applications.
You can also individually enable each of the PFI pins to output a
specific internal timing signal. For example, if you need the UPDATE*
signal as an output on the I/O connector, software can turn on the output
driver for the PFI5/UPDATE* pin.
DAQCard Clocks
Many functions performed by the DAQCard E Series cards require a
frequency timebase to generate the necessary timing signals for
controlling A/D conversions, DAC updates, or general-purpose signals
at the I/O connector.
A DAQCard can directly use its internal 20 MHz timebase as the
primary frequency source.