Chapter 5 POU and Task (2) Timer Interrupt For POU assigned to a task with timer interrupt, the function is similar to the subroutine of timer interrupt. When the timer interrupt has reached its time, all the POUs assigned to this task is executed according to the combination order. The task number with timer interrupt depends on the type of PLC used. In addition, the selected PLC type also determines the number of task group with timer interrupt based on the support of interrupt source groups. (3) Condition for Interrupt interrupt and etc. Since different types of PLCs provides different interrupt service and amount. Thus, users There are several types of condition for interrupt.
For example, external interrupt, I/O interrupts, count have to make sure which interrupt modes are supported by the selected PLC type. When POU is allocated to task with condition for interrupt, the function is similar to subroutine interrupt. When the condition for interrupt is formed, for example the count has reached setting value, then all the POU assigned to that task will execute in order. For AS5xx and DVPxxMC series, a POU can assign to multiple tasks and the same POU can repeatedly assign to the same task. While one task can assign to more than one POU and the allocated POU can also assign the execution order in the task.
Three ways regarding AS5xx/ DVPxxMC series task operation include freewheeling, cyclic and triggered by event. The following introduces ways of task operation and execution according to priority. Task Operation (1) Freewheeling The task is handled as soon as the program running starts. The task will be restarted automatically in the next cycle after one execution cycle ends. Executing freewheeling task: Priority High Free whe eli ng tas k System processin g Low task execution time 2 may not be equal in the above figure Note: There is no fixed execution time for the freewheeling task.
So the values of task execution time 1 and 5-7 Task execution time 1 IO User program Syst em p ro ces Task execution time 2 IO User program Syst em sing p ro cess IO User program IO User program sing Syst em p ro ces Syst em p ro cess