RSLogix5000 v16 - Unavailable Instructions within Add-Ons

tvey

Lifetime Supporting Member
Join Date
Mar 2005
Location
Halifax, NS
Posts
99
The help file for RSLogix 5000 v16 mentions several instructions that cannot be used within a custom Add-On:
Code:
JSR	Jump to Subroutine
               SBR	Subroutine
               RET	Return
               JXR	Jump to External Routine
               FOR	For (For/Next Loop)
               BRK	Break
               SFR	SFC Reset
               SFP	SFC Pause
               IOT	Immediate Output
               EVENT	Event Task Trigger
That being said, I created a test Add-On to convert Gray code to Binary using a structured text 'For' loop. It seems to work (using the emulator):
Code:
Binary.15 := Gray.15;
            
            for i:=14 to 0 by -1 do 
            	Binary.[i] := Binary.[i+1] XOR Gray.[i];
            end_for;

So why does this work? I don't have a chassis handy at the moment so I'm unable to test on an actual processor.

I have a couple of Add-Ons in mind that could make good use of the occasional For-loop. I'm a bit leery of proceeding unless I can be sure of consistent operation.

Attached is an exported copy of the test Add-On (remove the .txt extension to import).

-Trevor
 
In ladder, the FOR instruction has to call a separate routine. It doesn't loop within a routine (like on a PLC5). You can still loop using JMP and LBL instructions.

From the list, it appears that the add-on's must be completely self-contained - i.e. no code execution outside of the add-on.
 

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