String conversion question

Contr_Conn · Nov 13, 2005

Need a little help. All below is for Logix PLC.

I have an array of integers named INT[20], size may be different using 20 as an example.
I need to put these integers sequentially in the string named STR

Looks simple right?
COP INT[0] STR.DATA[0] 40
MOV 40 STR.LEN

Now the tricky part: the operation above will pack String in “Little-Endian” byte format:
Lo[0], Hi[0], Lo[1], Hi[1]…

The string I need is “Big-Endian” byte format:
Hi[0], Lo[0], Hi[1], Lo[1]…
The only way I found is a loop something like this:

Small correction - Source B in LES should be 19

Any ideas for a simple solution?
Thanks.

Contr_Conn · Nov 14, 2005

Post slided down with no response...

Any ideas?

Gerry · Nov 14, 2005

I don't think you can make it much simpler.

But you could use a DINT array to cut the number of loops in half. And the copy to the string could be done outside the loop, eliminating the MUL and INT_temp and index2.

Contr_Conn · Nov 14, 2005

DINT array is a good idea:
copy INT array to DINT first and do 2 conversions in one loop.
I'll try it tomorrow.

The only problem I see INT array size can be ODD
and as small as 1 word. Largest size 125 Integers.

ndzied1 · Nov 14, 2005

Sounds like a great job for structured text. Is that available on your processor?

TConnolly · Nov 14, 2005

Looks good to me. My only suggestion is to implement it in ST and use a FOR instruction instead.

Contr_Conn · Nov 14, 2005

ST may be better here, but it will not make it short.
I think I have no way to avoid a loop.
Question is how to make this loop most efficient.

I am using ControlLogix and ST is available in my RSlogix5000 package

But this sample should be available for all users and not every package included ST.

Alan Case · Nov 14, 2005

That sort of code should never fail or need modifying so put it in an ST, no-one should ever need to access it for maintainance.
Regards Alan Case

LadderLogic · Nov 14, 2005

SLC500 SWP instruction will swap low and high bytes in multiple words, say, 40 at a time.

Am I correct understanding that CLX swap instruction can handle only one word at a time? If so, this looks like a major step back...

String conversion question

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