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Chapter 2 Function Reference — AO_Change_Parameter
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National Instruments Corporation 2-29 NI-DAQ FRM for PC Compatibles
For the VXI-AO-48XDC device the
paramID
of
ND_OUTPUT_TYPE
is used in conjunction
with the channel value to select the analog output channel to be affected. To select a voltage
channel, set the
paramValue
to
ND_VOLTAGE
. To select a current channel, set the
paramValue
to
ND_CURRENT
.
FIFO Transfer Condition
You can specify the condition that causes more data to be transferred from the waveform
buffer into the analog output FIFO. NI-DAQ selects a default setting for you, in order to
achieve maximum performance. However, by changing this setting, you can force the FIFO
to remain as full as possible, or effectively disable, or reduce the size of the FIFO.
For example, to reduce the FIFO lag effect (the amount of time it takes data to come out of
the FIFO after being transferred into the FIFO), you can change the FIFO transfer condition
to FIFO empty. Notice that reducing the effective FIFO size can also reduce the maximum
sustainable update rate.
To change the FIFO transfer condition, set
paramID
to
ND_DATA_TRANSFER_CONDITION
,
and set
paramValue
to one of the values shown in Table 2-5:
Set
channel
to one of the channel numbers in your waveform group. For example, if you have
configured group 1 to contain channels 0 and 1, you can set
channel
to 0 or 1.
Note
This option is valid only for PCI E Series devices.
Table 2-4.
Voltage or Current Output Parameters
Device Type
Per Channel
Selection Possible
Legal Range for
paramValue
Default Setting for
paramValue
PC-AO-2DC
DAQCard-AO-2DC
VXI-AO-48XDC
Yes
ND_CURRENT_OUTPUT
and
ND_VOLTAGE_OUTPUT
ND_VOLTAGE_OUTPUT
Table 2-5.
Parameter Values for FIFO Transfer Conditions
Transfer Condition NI-DAQ Constant
FIFO not full
ND_FIFO_NOT_FULL
FIFO half-full or less
ND_FIFO_HALF_FULL_OR_LESS
FIFO empty
ND_FIFO_EMPTY
FIFO half-full or less until full
(DMA only)
ND_FIFO_HALF_FULL_OR_LESS_UNTIL_FULL