The NJ-series controller has two types of tasks:

• Primary periodic tasks (1 total)
• Periodic tasks (3 total) 

These task types have different execution conditions and execution order that allow the user to prioritize different controller functions such as I/O refreshing, motion control and specific program execution.
 

For example, critical functions such as motion control and critical I/O refreshing may need highest priority due to speed and performance. While indicator lights or data calculations can be assigned a lower priority if timing is not critical. With this type of configurability, system operation can be tailored to maximize consistent and efficient machine operation.

How does the NJ-series CPU execute tasks?

Both the primary periodic task and periodic tasks execute within a fixed amount of time. A primary periodic task executes within a fixed time such as 500μS. The periodic task execution also executes within a fixed amount of time, however the frequency can be adjusted in multiples of the primary periodic task period, i.e.1000/2000/3000/4000μS (2x,4x, 6x, 8x and higher). The example below illustrates a configuration where the primary periodic task is set to execute every 500μS and a periodic task is set to execute every 2000μS (4x the primary periodic task period).

IO: I/O refreshing
UPG: User Program
MC: Motion Control

*A double line indicates all processing for that task has completed

As shown in the illustration above, the primary period task always gets the highest priority and should be reserved for high performance, time-critical functions. Consequently, the primary periodic task is never interrupted. The periodic task(s) can be interrupted, but is guaranteed to complete within the allotted task period as shown.

Various controller functions can be assigned to the primary periodic task or periodic tasks, but some limitations exist. Refer to Cat. No. W501, NJ-series CPU Unit Software User's Manual for more details on settings, specifications, performance and procedures.