Trying to Improve my Programing.

Can someone explain to me the proper use or sinerio to use a timer timing (TT) versus the timer enabled (EN) bit is RSLogix 500.

Thanks,
Bob

I use the Timer Timing (TT) bit in parallel to an enabling condition for the timer when I expect the enabling condition to go away before the time is done but I want a full timing condition.

Suppose you want an output to be on for 20sec. You could use the timer timing bit. The TT is essentially the EN and NOT DN.

If I understand???

Currently I when a certain rung is true, I latch the timer and then use the (DN) bit to unlatch. If I understand you both, I can eliminate the latch bit and use the (TT) bit as bernie stated and when the timer (ACC) = (PRE) the (TT) will go false. This will then eliminate my need for the latch/unlatch and the use of the (DN) bit in the logic.

Thanks,
Bob

Bits are bits

Bob,
It depends on what you are trying to achieve as to what bit is best to use. TT is only true while the timer is timing and while the timer is enabled. If your timer rung goes false before acc=pre then the timer will stop and the EN and TT bit will go false. Of course this is in reference to the TON and RTO of the AB instruction set. How you use bits, including the DN bit are up to you and your sense of what is most simple to achieve your purpose. Understanding the bits and how they behave takes time and usage. Experiment if you have the chance especially if you have training software like LogixPro.

For TON or RTO:

    EN       DN              TT

---] [------]/[-------------( )--

For TOF:

     EN       DN           TT

----]/[------] [----------( )---