Indirect addressing using Logix5000

DairyBoy · Mar 24, 2011

Good day all. I think I've got it but please put me right if not. (More than likely). If I set up an integer (call it "array") with a non-zero value in dimension 0, can I use a pointer in an indirect move instruction to read/write to/from Array[0], Array[1], etc in the tag directory? is it that simple?

Thanks.

TConnolly · Mar 24, 2011

Yep.

MOV MyArray[Pointer] MyArray[(Pointer+1)]

DairyBoy · Mar 24, 2011

Thanks. Now I'm getting greedy: I can see the effect of making DIM1 "2" and figure that my indirect address would still work up to the end of the first "half" (Array[0,n] but how to access the "Array[1,n] data? Is this "multiple" indexing?

BillRobinson · Mar 24, 2011

Note, you can't do this with function blocks, only with ladder and structured text. Not sure with the other languages.

DairyBoy · Mar 24, 2011

That's ok, Bill. Ladder's enough for me

DairyBoy · Mar 24, 2011

Movin' on... In RSL500, if I want to enable a single bit in say, a B3 group via indirect addressing, I'll use an unconditionally enabled coil and address it B3:[N7:0] but I've tried the "equivalent" with an integer tag in square brackets following a BOOL32 tag and the RSL5000 editor won't allow more than one tag in the address field for the coil instruction. Is this format permitted in 5000?

daba · Mar 24, 2011

DairyBoy....

An array in Logix5000 can have 1 to 3 dimensions.

Any and every dimension index can be another tag, it can even be an expression....

e.g. suppose you have a 2-dimensional array called Data[x,y]

You can use...

Data[5,8]
Data[tagA,tagB]
Data[tagA+3,tagB*2]
Data[tagA,tagB-tagA]

Just about anything you want, so long as the expressions keep the calculated indices within the array dimension boundaries.....

daba · Mar 24, 2011

Not sure I understand your last post - are you trying to create a 2-dimensional BOOL array ?

DairyBoy · Mar 24, 2011

daba, In RS500 style: -----(B3:[N7:0])- so that if N7:0 is holding a value of 5, then B3:0/5 will be enabled.
So I've got a BOOL32 tag called "STEP" which represents STEP[0] to STEP[31] and an integer called "STEP_NUMBER". What I'm aiming to do is replicate the RS500 coil addressing above as: ---(STEP[0][STEP_NUMBER])- Is this appropriate?

daba · Mar 24, 2011

OK, I don't understand what a BOOL32 tag is, but.....

If I understand correctly you want to turn on a single BOOL element of a BOOL array tag ?

Tag STEP; Data-Type BOOL[32]
Tag STEP_NUMBER; Data-Type DINT

If STEP_NUMBER = 15

Then OTE STEP[STEP_NUMBER] will turn on STEP[15]

Addendum : Use DINTs in preference to any other integer data-type, even if you only want to hold a number value 0-31. It may seem excessive, but the processor will only have to convert SINTs or INTs to DINTs to use them, and the smaller data-types still occupy 32 bits of memory anyway.

DairyBoy · Mar 24, 2011

Thanks daba, I've got it now.

daba · Mar 24, 2011

welcome

DairyBoy · Mar 24, 2011

Almost there but getting a compile error. Looks ok to me though... EDIT: I missed the third index value. In this case it's a zero. Oops! Time for bed.

lostcontrol · Mar 25, 2011

daba said:
DairyBoy....Just about anything you want, so long as the expressions keep the calculated indices within the array dimension boundaries.....

Take heed of this statement, else you will have trouble..

daba said:
OK, I don't understand what a BOOL32 tag is,
Addendum : Use DINTs in preference to any other integer data-type, even if you only want to hold a number value 0-31. It may seem excessive, but the processor will only have to convert SINTs or INTs to DINTs to use them, and the smaller data-types still occupy 32 bits of memory anyway.

Someone has said to me that you can see the memory that each tag has, is this possible?

DairyBoy · Mar 25, 2011

Lostcontrol, Re Take heed: I triple-check for this one these days. Crashed a whole plant running from one plc when I was forced to reduce the size of some data tables in an slc504 to accommodate prog mods. Live and learn!

Indirect addressing using Logix5000

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