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Chapter 3
Hardware Overview
3-12
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National Instruments Corporation
This figure shows that CONVERT* can be generated from a number of
sources, including the external signals RTSI<0..6> and PFI<0..9> and
the internal signals Sample Interval Counter TC and GPCTR0_OUT.
sources, including the external signals RTSI<0..6> and PFI<0..9> and
the internal signals Sample Interval Counter TC and GPCTR0_OUT.
Many of these timing signals are also available as outputs on the RTSI
pins, as indicated in the
pins, as indicated in the
section later in this chapter, and
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.
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.
Board and RTSI Clocks
Many functions performed by the 611X E board 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.
timebase to generate the necessary timing signals for controlling A/D
conversions, DAC updates, or general-purpose signals at the I/O
connector.
The 611X E board 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.
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.
PCI_E.book Page 12 Thursday, June 25, 1998 12:55 PM