ISPSoft User Manual 5.3 Tasks Every POU of the program type is assigned to a specific task. The tasks determine the order in which the POUs of the program type are executed or enabled. The Task is like a mission. In other words, every POU of the program type is like a basketball player, and the tasks are the roles that the POUs play. 5.3.1 Managing the Tasks in ISPSoft In ISPSoft, not all the POUs of the program type in the project are executed. A POU of the program type will be executed after it is assigned to a task, and the task determined how the POU is executed.
When a POU is not assigned to a task, the POU is refer to as a source code saved in a project, but not to be translated into an execution code. Only POUs of the program type need to be assigned to tasks, and function blocks are called by POUs. The characteristic of the IEC 61131-3 architecture is that a program is divided into several independent POUs. All POUs are rearranged to scan as execution code for compiling and the combination is based on the TASK allocation status.
In ISPSoft, a POU is assigned to one TASK, however, only DVPxxMC and AS5xx series can assign a POU to multiple tasks, but the same task can allocate to more than one POU and the allocated POU can also assign the execute order in task; when users add a POU, a task has to be assigned by default. For AS, AH and DVP series, the TASK operation can be categorized into three types: Periodic, Timer Interrupt and Condition for Interrupt. (1) Periodic For POU assigned to periodic task, the execution is simply to scan back and forth.
Since there is only one periodic task in DVP series, therefore, all POUs been periodically scanned are assigned to this task; while AH series provides 32 periodic tasks for selection with number from 0 ~31. The scanning starts with small number as number one priority and AH series supports API command (TKON and TKOFF) to control task. Users can adopt the command to activate or stop a task during PLC operation. The POU is created in SFC language and can only be allocated in periodic task and not task with interrupts.
5-6 Applicable AS/AH/DVP AS5xx/DVPxxMC Work Management A POU is assigned to one task A POU is assigned to multiple tasks Operation Periodic, Timer Interrupt and Condition for Interrupt Freewheeling ,Cyclic and Triggered by Event