A-B PLC5 addresting question

CDF1909

Member
Join Date
Nov 2003
Location
Mason, Ohio
Posts
15
I am trying to follow the ladder logic in an A-B PLC 5/80, I'm using RSLogic 5, ver. 6.30.
I'm trying to find where and how some data is stored. I come accross several address, the format I dont understand.
Such as an "ADD" instruction Add Source A N[N27:0]:59
Source B N27:4
DEST N27:60
I don't understand the address for Source A, ie the brackets.

Will someone please enlighten me to how this address works?
 
Never seen an AB PLC, nor it's software, but from what I've gathered reading posts, that looks alot like indirect adressing

Think it's best explained as -> N[value of N27:0]:59
N27:0 contains a value, lets say 26, then the first destination address could also be written as: N26:59

But then again I could be wrong...;)
 
Jeebs nailed it - even without ever seeing the AB software! ... the demo in this post won't give a better explanation than the excellent one that Jeebs has already given - but it might make it easier to work with the software ...
 
Jeebs said:
Never seen an AB PLC, nor it's software, but from what I've gathered reading posts, that looks alot like indirect adressing

Think it's best explained as -> N[value of N27:0]:59
N27:0 contains a value, lets say 26, then the first destination address could also be written as: N26:59

Good job! This is how it works.

Watch out - most likely N27:0 is changed within the program. Then the indirect address would change.
 
Thanks;

Ok I have seen the light. The way Jeebs explained it,and the post that Ron pointed to were both helpful.
Yes, Oakley the value of N27:0 is changed in several places in the program. That was one of the reasons I had a hard time following it.
 

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