Chapter 14
Onboard Programs
14-2
ni.com
Using Onboard Programs with NI 73
xx
Motion Controllers
You can use the real-time operating system on the NI 73
xx
motion
controller to run custom programs. This functionality allows you to offload
some motion-specific tasks from the host processor and onto the motion
controller. Using onboard variables, which are global data on the device,
arithmetic and loop operations, and efficient wait functions, you can write
onboard programs to execute parts of the motion application with almost
no host interaction. You can execute up to 10 onboard programs
simultaneously.
Onboard programs have the least priority in a preemptive multitasking
environment running on the embedded microprocessor because the primary
function of the embedded processor is supervisory control and I/O reaction.
Instead, the onboard programs run in a time-sliced manner at the lowest
priority. Each onboard program gets a default time slice of
two milliseconds, after which it relinquishes control of the processor to the
next onboard program or housekeeping task.
The host communication and I/O reaction tasks take higher priority than the
onboard programs and housekeeping tasks, as shown in Figure 14-1.
The onboard programs and housekeeping tasks are time-sliced among
themselves.
For greater control and determinism for the motion control system,
National Instruments offers the LabVIEW Real-Time (RT) module motion
control system, which consists of a PXI chassis, PXI motion controller or
controllers, LabVIEW RT, and NI-Motion driver software.
