Control Bits within RS Logix

whenever i ask a question like this i feel like a fool. i am unsure what the use or need for a control bit in RS logix is. i know where to use them etc but....what do they actually do.

cheers

What "Control Bit" are you talking about?

i mean the data table labelled R6. i am so unsure what they are i cannot even describe them. they are used in sequencers. under the control heading that you have to specify.



Highlighted is the data table i refer to.

cheers

Those are control elements. they are made up of words and bits, like timers and counters.

Open the data table (double click) and look at it.

They are used with instructions like SQO, SQI, and many others.

That should get ya started...

Paul

/nod. Okay. As Okie stated, they are actually data structures, that maintain specific information required for many instructions in the program. Just as a timer has to maintain it's status bits, preset value, and accumulated value, other instructions need to keep track of their operation.

Mostly, the Control Files are used for sequential operations like FSC (File Search and Compare), Shift Registers, just about all FILE class instructions, as a matter of fact. The "Control" data block maintains the working length of it's data set, the current position being processed, and again, status bits.

oh i see, i just had a look on one of the programs we have and i can see whatyou mean. i think its gonna take some time for me to completely understand it but i will not bore you clever people i will do some leg work of my own.
thanks for the help

Look at it this way, a timer, or counter needs a way of knowing when it is done, and what it's current count and target counts are.

All of the File operations also need a place to store their current postion. In the example of an FSC instruction, the instruction must be able to step, one element at a time, through a block of data, of some arbitrary length, to see if a compare is true (or not).

Now, just as with a timer where you could maintain your own accumulator, and preset, and status bits, and increment and compare against a known time source like the CPU Real time Clock, you could yourself write a FOR/NEXT loop, with register to indicate where you are, and what the end of the search array is, and JMP out setting a flag if a search target is found.

Kind of easier to let the PLC itself deal with the details

ah ok! that makes sense. an from the sounds of it, yea is kinda easier to let the PLC do its thing.

thanks for the explanation

having had a play i can see what you mean completely now.

cheers