National Instruments NI USB-621x - Manual (Page 74)

Chapter 7 Analog Output
© National Instruments Corporation 7-7 NI USB-621x User Manual
The source also can be one of several other internal signals on your DAQ
device. Refer to Device Routing in MAX in the NI-DAQmx Help or the
LabVIEW 8.x Help for more information.
You also can specify whether the samples are paused when ao/PauseTrigger
is at a logic high or low level.
AO Sample Clock Signal
Use the AO Sample Clock (ao/SampleClock) signal to initiate AO samples.
Each sample updates the outputs of all of the DACs. You can specify an
internal or external source for ao/SampleClock. You also can specify
whether the DAC update begins on the rising edge or falling edge of
ao/SampleClock.
Using an Internal Source
One of the following internal signals can drive ao/SampleClock.
• AO Sample Clock Timebase (divided down)
• Counter n Internal Output
A programmable internal counter divides down the AO Sample Clock
Timebase signal.
Using an External Source
Use the external signals PFI <0..3> or PFI <8..11> as the source of
ao/SampleClock.
Routing AO Sample Clock Signal to an Output
Terminal
You can route ao/SampleClock (as an active low signal) out to any
PFI <4..7> or PFI <12..15> terminal.
Other Timing Requirements
A counter on your device internally generates ao/SampleClock unless you
select some external source. ao/StartTrigger starts the counter and either the
software or hardware can stop it once a finite generation completes. When
using an internally generated ao/SampleClock, you also can specify a
configurable delay from ao/StartTrigger to the first ao/SampleClock pulse.
By default, this delay is two ticks of ao/SampleClockTimebase.