Ao Sample Clock Timebase Signal; Master Timebase Signal - National Instruments 6711 User Manual

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AO Sample Clock Timebase Signal

You can select any PFI or RTSI pin as well as many other internal signals as the AO Sample
Clock Timebase (ao/SampleClockTimebase) signal. This signal is not available as an output on
the I/O connector. The ao/SampleClockTimebase is divided down to provide the Onboard Clock
source for the ao/SampleClock. You specify whether the samples begin on the rising or falling
edge of ao/SampleClockTimebase.
You might use the ao/SampleClockTimebase signal if you want to use an external sample clock
signal, but need to divide the signal down. If you want to use an external sample clock signal,
but do not need to divide the signal, then you should use the ao/SampleClock signal rather than
the ao/SampleClockTimebase. If you do not specify an external sample clock timebase, NI-DAQ
uses the Onboard Clock.
Figure 3-9 shows the timing requirements for the ao/SampleClockTimebase signal.
Figure 3-9. ao/SampleClockTimebase Timing Requirements
t
p
t
t
w
w
t = 50 ns minimum
p
t = 23 ns minimum
w
The maximum allowed frequency is 20 MHz, with a minimum pulse width of 10 ns high or low.
There is no minimum frequency.
Unless you select an external source, either the 20MHzTimebase or 100kHzTimebase generates
the ao/SampleClockTimebase signal.

Master Timebase Signal

The Master Timebase (MasterTimebase) signal, or Onboard Clock, is the timebase from which
all other internally generated clocks and timebases on the board are derived. It controls the
timing for the analog output and counter subsystems. It is available as an output on the I/O
connector, but you must use one or more counters to do so.
The maximum allowed frequency for the MasterTimebase is 20 MHz, with a minimum pulse
width of 23 ns high or low. There is no minimum frequency limitation.
The two possible sources for the MasterTimebase signal are the internal 20MHzTimebase signal
or an external signal through RTSI 7. Typically the 20MHzTimebase signal is used as the
MasterTimebase unless you wish to synchronize multiple devices, in which case, you should use
Real-Time System Integration Bus (RTSI), for more information on
RTSI 7. Refer to Chapter 8,
which signals are available through RTSI.
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