Acquiring Time-Sampled Position And Velocity Data - National Instruments NI-Motion User Manual

Acquiring Time-Sampled
Position and Velocity Data
© National Instruments Corporation
NI motion controllers can acquire a buffer of position and velocity data that
is firmware-timed. After you command the motion controller to acquire
position and velocity data, a separate acquire data task is created in the
real-time operating system that reads time-sampled position and velocity
data into a FIFO buffer on the motion controller. You can read data in from
this buffer asynchronously from the host computer, as shown in
Figure 11-1.
The acquire data task has higher priority than any onboard programs or
housekeeping tasks, but it has a lower priority than the I/O reaction and host
communication tasks. To achieve the best possible performance, keep host
communications to a minimum when acquiring data.
11-1
Step 1: Reads the
position velocity
Acquire data task
Step 2: Copies position and
velocity data to FIFO buffer
Step 3: Reads data from
the buffer asynchronously
Figure 11-1. Acquire Data Path
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NI-Motion User Manual