National Instruments NI-Motion - Manual (Page 145)

© National Instruments Corporation 11-1 NI-Motion User Manual
11
Acquiring Time-Sampled
Position and Velocity Data
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.
Figure 11-1. Acquire Data Path
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.
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