Chapter 3
Hardware Overview
PCI-6023E/6024E/6025E User Manual
3-8
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National Instruments Corporation
UPDATE* signal as an output on the I/O connector, software can turn on
the output driver for the PFI5/UPDATE* pin.
Board and RTSI Clocks
Many board functions 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.
These boards can use either its internal 20 MHz timebase or a timebase
received over the RTSI bus. In addition, if you configure the board to use
the internal timebase, you can also program the board to drive its internal
timebase over the RTSI bus to another board that is programmed to receive
this timebase signal. This clock source, whether local or from the RTSI bus,
is used directly by the board as the primary frequency source. The default
configuration at startup is to use the internal timebase without driving the
RTSI bus timebase signal. This timebase is software selectable.
RTSI Triggers
The seven RTSI trigger lines on the RTSI bus provide a very flexible
interconnection scheme for any PCI E Series board 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 3-4.
PCI.book Page 8 Wednesday, September 16, 1998 9:09 AM
