National Instruments AT E Series - Manual (Page 46)

Chapter 3 Hardware Overview
AT E Series User Manual 3-20 ni.com
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. To use the PFI pins as outputs, you must use the Route
Signal VI to individually enable each of the PFI pins to output a specific
timing signal.
Device and RTSI Clocks
Many functions performed by the AT E Series devices 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.
An AT E Series device can use either its internal 20 MHz timebase or a
timebase received over the RTSI bus. In addition, if you configure the
device to use the internal timebase, you can also program the device to
drive its internal timebase over the RTSI bus to another device that is
programmed to receive this timebase signal. This clock source, whether
local or from the RTSI bus, is used directly by the device as the primary
frequency source. The default configuration at startup is to use the internal
timebase without driving the RTSI bus timebase signal. You select this
timebase through software.
RTSI Triggers
The seven RTSI trigger lines on the RTSI bus provide a very flexible
interconnection scheme for any AT E Series device sharing the RTSI bus.
These bidirectional lines can drive any of eight timing signals onto the
RTSI bus and can receive any of these timing signals. This signal
connection scheme is shown in Figure 3-15.