Chapter 3
Analog Output
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National Instruments Corporation
3-11
Analog Output Series User Manual
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
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.
t
p
= 50 n
s
minim
u
m
t
w
= 2
3
n
s
minim
u
m
t
w
t
w
t
p
