Measurement Computing Data Acquisition Systems rev.10.4 - Manual (Page 212)

Update/Sample Data Format
The dataFormat parameter allows the selection of the format of the output sample data that applies to the
file. The file must have the its sample data formatted in one of the following valid formats in order to be used
for a waveform/pattern output from file operation. The while the layout of the output file is fixed, the format of
the output sample data can vary greatly. Several output sample data formats are available in both binary and
ASCII data formats.
Output From File Operation
Once the waveform/pattern output has been configured and the output from file has been setup using this
function, the waveform/pattern output operation can be armed using the daqDacWaveArm function. When
the waveform/pattern output operation is armed, the driver will transfer as much output data as possible to the
internal output FIFO on the device. Once the waveform/pattern output operation is triggered, the driver will
then refill the internal output FIFO as room becomes available from the specified output data file. The cycle
data transferred from the output data file to the internal output FIFO is read from the valid output cycle data
area defined by the file layout table in the “File Layout” section (unshaded update cylces)
Output
FIFO Header Info Offset Cycles Valid Data Cycles Unused Cycles
While the waveform/pattern output operation is active, the driver will continue to fill the internal output FIFO
with output cycle data until the waveform/pattern output termination condition is satisfied. The
waveform/pattern output termination is configured by setting the appropriate update mode using the
daqDacWaveSetMode
function. Once cycle data is transferred to the internal output FIFO on the device,
the device is responsible for maintaining the output FIFO and updating the output channels every update clock
pulse. When the output update clock “fires”, the next available update data block is loaded from the internal
waveform/pattern output FIFO on the device to the port, which then presents the values to the DAC or digital
port for output.
Data Presented to Outputs
DAC0 DAC1 DAC2 DAC3 P3 DO DAC0 DAC1 DAC2 DAC3 P3 DO
Update clock (Update Cycle 0) Update clock (Update Cycle 1)
Processing Output FIFO
The status of a waveform/pattern output operation can be monitored using the daqDacTransferGetStat
function. When in waveform/pattern output-from-file mode, the retCount parameter indicates the number of
iterations of the file and not the total number of update cycles.
The amount of data transferred of the will automatically calculate the number of complete output update cycles
in the file using the offset information, the number of channels currently configured for waveform/pattern
output, the size of the data samples and the total file size.
4.4-30 Daq API Command Reference 908494 Programmer’s Manual