National Instruments 6711, Руководство пользователя

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Chapter 3 Hardware Overview
6711/6713/6715 User Manual 3-6 www.ni.com
Figure 3-3 shows that you can generate UPDATE* 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.
Many of these timing signals are also available as outputs on the RTSI pins,
as indicated in the RTSI Triggers section later in this chapter, and on the
PFI pins, as indicated in Chapter 4,
Signal Connections .
Programmable Function Inputs
♦
6711/6713
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 you can use any of the PFIs
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.
Device and RTSI Clocks
♦
6711/6713
Many functions performed by the 6711/6713 device require a frequency
timebase to generate the necessary timing signals for controlling DAC
updates or general-purpose signals at the I/O connector.
The 6711/6713 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. This timebase is
software selectable.
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