RSlogix 5k Timers question

Hi All

In my program ladder i have a routine called from main:

main
---------------JSR MyFunc

MyFunc

Cond
--||----------RET

--------------TON

If Cond = True, the routine returns and the timer stops
however when Cond = False TON should continue from the point
it stopped,but that doesnt happen.
It seems that it continues to count and when Cond = False
it shows the time already past.

Why?

You always need to be a little careful of timers in conditional subroutines, or more correctly in your case, an unconditional subroutine with a conditional return.

A timer programmed this way will never be updated as false. the timer instruction needs to see at least one scan where the input conditions to itself are false in order to properly set the enable bit. Since you are leaving the subroutine the timer instruction never sees the false input case. So it continues on as if it is still running.

There is a limit to how long you can go between timer services and still maintain accuracy. I don't know that value off the top of my head but it is out there.

Keith

If you wish the timer to reset on COND=False then place the timer before the RET. Enable the timer using the same condition.

If you want the timer to start from where it left off you should use a RTO instead of a TON. A Retentive timer will pick up where it left off.

Hi

RTO wont work in this case (i tried it) since the difference
between RTO and TON is valid whilst there is a condition in the input.

The solution is to keep the value of .ACC before returning.

That is sooo bogus!

Why would you want to do this that way?

Bernie gave an answer to your problem.

RSL

Hi

I see that keeping the .ACC value before returning doesnt work
either.

The purpose of this was to skip doing the folowing rungs
when a condition term apply.