Reset a word to 0000000000

Hi guys,
How do I reset a word to 0000000000. I am using it to contain data from a bit shift instruction and want to be able to zero it.

Thanks in advance.
Dazzz

Welcome to the Forum !

The precise instruction depends on the controller instruction set. Some use a Move instruction (to place a zero value into the word), some will use a Clear, and some will use a Multiply.

What model of controller are you using, and what is the data table or tag address format of the "word" register ?

XOR itself?

Hi guys, I worked it out by using a (res) with the word address eg: #B3:2

Cheers

How do I reset a word to 0000000000 ?

Click to expand...

I worked it out by using a (RES) with the word address eg: #B3:2

Click to expand...

In which case your original word was probably a 16-bit binary word, and your reset value would then be "0000 0000 0000 0000", not "00 0000 0000". Resetting all 16 bits is not exactly the same as setting the first 10 bits to 0. In some cases, there may be a need to preserve some of the original bits, so that they do not get reset to 0.

If you only want to reset 10 bits out of the 16-bit B3:2 as you first stated, you would need to use the MVM masked-move instruction.

Well we still don't know what platform he is using, and it must be a strange one with a 10-bit word !!

If we don't get the manufacturer, type, and version, I have to admit the generic answer was given by rootboy.

XOR'ing any data with itself will always reset all the data bits.

Back to the OP's question.....I initially thought, because I saw the address B3:2, it was PLC5 or SLC, but when I tried RES with the indexed address #B3:2 in an SLC program, the rung was not accepted.... see pic.

Which all goes to show that I have wasted my time trying to second-guess and answer a badly constructed question.....

And the OP has stated that his problem is solved, but there will be nothing to search on, because we still don't know what PLC he is using.

Hi Guys,
Sorry for the poorly constructed question. I am using a Micrologix 1000 and yes Lance I did mean "0000 0000 0000 0000".
Cheers

Then as daba pointed out, RESET will not work very well for a Binary B3 or Integer N7 word. It only works in the LogixPro Simulator because LogixPro does not duplicate the RSLogix software exactly. This is one of the differences of which you need to be aware.

Suggestion: CLR (Clear) and MOV (Move) work in both LogixPro and RSLogix to reset word values to 0.

RSLogix methods to reset a word value to 0.

At the risk of repeating myself, XOR it?

Supposedly this is the fastest way (machine cycle wise) to zero out a register in a CPU (be it a PLC or whatever).

Back in the day I suppose that it mattered. Nowadays, guys like Peter N. are going to be the only ones who need any of the speed benifits of XORing.

But it still works, and you don't have to concern yourself with the data type that you are trying to clear out (as long as the XOR statement will accept your parameters).

@Ken, be careful with multiplying. In some PLCs, that will zero out the next highest register as well. You might not want that...

Based on execution times, XOR is slower than either a MOV or a CLR. CLR is the fastest.

But realistically, or OP wasn't asking for the fastest way. Perhaps the method others will easily understand would be best.

OG

The CLR instruction is probably the fastest on a PLC because it only has one operand or memory access required. When I program in assembly language I usually XOR or SUB a register from itself. There is no need for a CLR instruction since either XOR or SUB will do.