SLC 500 Timer Time Base Memory Location

[gdshd]

Anybody out there know exactly where a timer's time base data is stored in memory for a SLC 500? Is it in the reserved portion of the timer element's status word? I have not yet run across this info.

 

[Ken Moore]

Each timer has three words, the first word contains the "control" bits, done, enabled, etc...
The time base is stored there, I believe in the SLC's it's bit 9, T4:0/9 for example. Since there only two choices in the SLC's only one bit is needed, I would guess the MLX line uses two bits, because of the additional time bases.

 

[Ron Beaufort]

Greetings gdshd ...

the response from my distinguished colleague Ken Moore is correct – but it still might not answer your question ...

before we go any further, here’s a question for you ... why do you want to know? ...

if it’s so that you can CHANGE the time base “on the fly” by having your ladder logic program toggle a bit in your program – then I doubt that you’re going to be successful in that enterprise ... the “time base” bit located in the timer’s “memory area” is more or less “read only” ... specifically, changing the status of the bit will NOT change the operation of the timer in any way ...

more specifically, if you’re trying to do what I THINK you’re trying to do, then you’re probably going to need to manually “edit” the TON instruction ...

going further ... if you try to control the bit T4:0/9 by using something like a simple OTE instruction, then you’ll probably get a notice like “Can’t access control word bits!” in the “Status Line” (lower left corner of RSLogix500 window) ... in other words, RSLogix500 won't normally allow you to go into that area of the timer’s memory ...

going ever further ... if you really and truly have your heart set on accessing that bit, we CAN tell you how to do it ... even so, whenever I toggle that bit on and off here in the lab, the timer’s operation does NOT change – and the “Time Base” displayed in the TON instruction does NOT change either ...

sorry if this sounds like it’s going in circles ... give us more information about what you’re trying to do and we’ll straighten it all out ...

and welcome to the forum ...

 

[gdshd]

I teach an intro PLC class @ a Community College in Indiana. I had an astute student in class ask where the TB was stored. Didn't have an immediate answer, but knew where to look. Have no intention of manipulating the TB bit status, but was curious to know since I had never run accross this info in my dealings. I had a strong suspicion it was stored here, but couldn't immediately confirm. Thanks for the quick response. This was my first time posting to Q&A. I think this will become a powerful learning tool. I greatly appreciate Ken and Ron's guidance in this matter. Thanks!

gdshd

 

[Doug-P]

May be a small point but,

The construction "bit T4:0/9" is illegal in PLC-5s and SLCs so I'm assuming it is in MLX also.

In those processors the correct syntax is: T4:0.ACC/9 if you're interested in the ACCumulated value of the timer and T4:0.PRE/9 to check the timer PREset values.

 

[Ron Beaufort]

I teach an intro PLC class @ a Community College in Indiana.

you might be interested in the "Offers for Instructors" button on my website menu ... just pick up the phone and give me a call ...

I think this will become a powerful learning tool.

exactly ... thanks to Phil ...

glad we were able to help ...