control builder f 800
thanks for reply me
well 1 st question is talking about tasks which is mentioned in manual (freelance product catalog9.2) exactly under chapter 4 controller page NO 18 the pragraph said "Different modes are available for user task execution:
−− Up to eight tasks with individual cycle times between 5 ms and 24 hours
−− Processing as fast as possible (PLC mode); one task only" I need to more clarification about these tasks (cyclic task, plc task)
as the second question I mean If I want make the imagination relay to hold the signal how can I make that
1) Cyclic tasks are always called at regular time intervals.
PLC Tasks are evently drive and called at some situation: "Stop", "Run", "Error" etc. It is executed once only .
2) If you want to hold signal (variable?) at start of a controller, then you must write a program where you write "1" to the variable and place it to the "Run" tab of the *.SYSTask container.
I hope, i help you.
Hope the task task i.e cyclic taks are straigh forward to you.
Here is more details about default taks(PLC mode) "PLC mode At most one user task can be made the default task, in that it computes in PLC mode. It has the lowest priority of all cyclic tasks, and starts itself again at once after a run. This leads to the fastest possible cyclic processing of the underlying programs. Because of its low priority (50) it can be interrupted by all other tasks. The default task is only in execution when no other task is ready to compute."
So as dima replied all process logic you can design under task task (cyclic task) and event base logics and initialisations you program under those system task.
Now if you use default task with task task possibility your default task get hang up or in wait to get executed because of lowest priority. hence recomended to use task task and design event base logics in system tasks that will be executed once.
I understand you are comparing PLC way of programming with DCS controller or in DCS program editor, where in PLC memory area is confined and well addressed and mapped to physicall I/O points, where as in DCS controller it is indirectly mapped via variable or via some referrence points and free from physicall I/O point association.
So to hold some output( in your case referring to relay), just map variable to that output and give value one even you can write logic when it should be one or zero programatically, other way manually you can force output permanantly one or zero in comissioning mode.
Hope this clarifies.
I see there is much confusion, so, although it was all said already, let me clarify.
The tasks in controller are divided into system tasks and user tasks.
The system tasks are event driven tasks that are used to create programs (like error handling programs) that run only with some system events (like cold start).
User tasks are tasks for user programs that control the process in the plant. There are TWO TYPES of user tasks: cyclic tasks (also called TASK) and PLC tasks (also called DEFAULT TASK). The cyclic task runs once in every task cycle (for example 500ms). It doesn't matter that the programs runtime is 15ms - if it's define inside cyclic task that has cycle of 500ms it will run for 15ms, wait 485ms and then run again.
Here is the main difference as in PLC task You don't have cycle time - it runs as fast as possible, so a program with runtime of 15ms in PLC task will run one full run after another (as long as there is no other program defined in his task and no other task starts).
As such the PLC task uses every ms of CPU idle time, becouse it runs always when no other task is running. Remember it's not always a good thing (the memory load is about 100%).
The Process Image variables are read only once (at the begining of the program run) and writen only once (when the progrma ends its run). Non-process imgae variables are read when needed.
I hope it made things a little bit clearer,