© National Instruments
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2-13
Hardware-Timed Single Point Acquisitions
Hardware-Timed Single Point (HWTSP) is a hardware-timed acquisition mode in which a
digital hardware signal (SampleClock) controls the rate of the acquisition. The SampleClock
signal can be imported or internally generated on the NI PXIe-4302/4303 using the sample rate
configured with a NI-DAQmx task.
During Buffered acquisitions, the device may wait to transfer data to the host machine to build
larger bus transactions. This optimizes throughput. During HWTSP acquisitions, the device
sends data to the host in response to every sample clock. This optimizes latency.
These features make HWTSP ideal for real-time control applications. HWTSP acquisitions, in
conjunction with the wait for next sample clock function, provide more deterministic
synchronization between the software layer and the hardware layer. Refer to the
NI-DAQmx
Hardware-Timed Single Point Lateness Checking
document for more information. To access
this document, go to
ni.com/info
and enter the Info Code
daqhwtsp
.
Hardware-Timed Single Point Acquisition Model
The HWTSP data path is optimized for low-latency applications and is different than the data
path used in buffered mode acquisitions.
When in HWTSP mode, the filtering and sampling systems can be modeled as being decoupled,
which allows you to configure the filter and sampling rate independently.
Figure 2-10 shows the HWTSP data path model.
Figure 2-10.
HWTSP Data Path Model
The ADC samples the input stream and returns it to the PXIe controller or computer based on
the SampleClock signal.
Maximum HWTSP Rate Analysis
During HWTSP acquisitions the maximum achievable acquisition rate without missing a sample
is affected by both the transfer and application time. Refer to Figure 2-11.
Note
HWTSP acquisitions can detect if they cannot keep up with the acquisition
rate. Refer to the
Hardware-Timed Single Point Sample Mode
topic in the
NI-DAQmx
Help
for more information.
PXIe Controller or Comp
u
ter
An
a
log Front End
Config
u
r
ab
le
Low P
ass
Filter
A/D
Rate
MAX
1
TransferTime ApplicationTime
+
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