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Chapter 5 Programming
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National Instruments Corporation 5-7 AT-MIO-16X User Manual
Reading a Single Conversion Result
A/D conversion results are available when ADCFIFOEF* is set in the
Status Register and can be obtained by reading the ADC FIFO Register.
To read the A/D conversion result, use the following steps:
1. Read the Status Register (16-bit read).
2. If the OVERRUN or OVERFLOW bits are set, an error occurred
and data was lost.
3. If the ADCFIFOEF* bit is set, read the ADC FIFO Register to
obtain the result.
Reading the ADC FIFO Register removes the A/D conversion result
from the ADC FIFO and clears the ADCFIFOEF* bit if no more values
remain in the FIFO.
The ADCFIFOEF* bit indicates whether one or more A/D conversion
results are stored in the ADC FIFO. If the ADCFIFOEF* bit is not set,
the ADC FIFO is empty and reading the ADC FIFO Register returns
meaningless data. Once an A/D conversion is initiated, the
ADCFIFOEF* bit is set approximately 10 the conversion, indicating
that the data conversion result can be read from the FIFO.
An ADC FIFO overflow condition occurs if more than 512 conversions
are initiated and stored in the ADC FIFO before the ADC FIFO Register
is read. If this condition occurs, the OVERFLOW bit is set in the Status
Register to alert you that one or more A/D conversion results have been
lost because of FIFO overflow. Strobing the DAQ Clear Register resets
this error flag.
An ADC overrun condition occurs if an attempt is made to start a new
conversion while the previous conversion is being completed. If this
condition occurs, the OVERRUN bit is set in Status Register 1 to
indicate an error condition or that an invalid operation occurred.
Strobing the DAQ Clear Register resets this error flag.
Programming Single-Channel Data Acquisition Sequence
The following programming sequence for sample counts less than
65,537 leaves the data acquisition circuitry in a retriggerable state. The
sample-interval and sample counters are reloaded at the end of the data
acquisition to prepare for another data acquisition operation. The
counters do not need reprogramming, and the next data acquisition
operation starts when another trigger condition is received.