Chapter 5 Programming
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National Instruments Corporation 5-21 AT-MIO-16X User Manual
7. Entries stored in the mux-channel gain memory should be scanned
once during a scan interval. The following condition must be
satisfied:
scan interval ≥ sample interval * x, where x is the number of entries
in the scan sequence.
Write the desired scan interval to the Am9513A Data Register to
store the Counter 2 load value:
– If the scan interval is between 2 and FFFF (65,535 decimal),
write the scan interval to the Am9513A Data Register.
– If the sc an in terv al is 10000 ( 65,536 de ci mal), w rite 0 to the
Am9513A Data Register.
8. Write FF22 to the Am9513A Command Register to arm Counter 2.
After you complete this programming sequence, Counter 2 is
configured to assign a time interval to scan sequences once the trigger
to enable A/D conversions is detected.
Applying a Trigger
Once a data acquisition operation has been configured and
programmed, the acquisition sequence is initiated when a trigger is
received. A trigger can be initiated through software or hardware.
To initiate the data acquisition operation through software, strobe the
Start DAQ Register. Make sure EXTTRIG* is not pulled low at the I/O
connector or the RTSI switch.
To initiate the data acquisition operation through hardware, apply an
active low pulse to the EXTTRIG* pin on the AT-MIO-16X I/O
connector. See the Timing Connections for Data Acquisition and
Analog Output section in Chapter 2, Configuration and Installation,
for EXTTRIG* signal specifications.
Once the trigger is applied, Counter 3 generates pulses initiating A/D
conversions once every sample interval until the sample counter
reaches zero. In the pretrigger mode, these conversion s are not counted
by the sample counter. Counting begins only after the application of a
second hardware or software trigger condition and continues until the
sample counter reaches zero. A/D conversion data stored bef ore receipt
of the EXTTRIG* or DAQ Start signal are pretrigger samples.