Digital Link Input is not working properly

[Ramil.R]

Hello,

We have two identical SLC 500 PLCs, one for each package. Part of the programs of one of them is not working properly. Both projects are identical except for tag numbers.
So, Digital Link Input is not working properly in the second PLC (image 2). The coil does not react when its contact's corresponding bit has a value of 1. It only happens in the Digital Link Input parts of INPUT_MAP.
Could anyone help me why it happens?

Thanks in advance

 

[parky]

It could be that the output bits are used elsewhere do a cross reference, as the link bits are shown as true it could be those output bits are being turned off elsewhere or the call to that block is not being enabled.

 

[chelton]

Is Lad 3 being executed every scan or is it conditional?
Is B3:101/1 or /3 unlatched before the end of the program?

 

[Engineerj22]

I would make sure that there's a JSR to LAD 3.

 

[Ken Roach]

Welcome to the PLCTalk forum community ! Are you really in Azerbaijan or was that an accident of alphabetization when you registered ?

I agree that the two most likely explanations are a duplicate address conflict or that LAD3 is not being called by a JSR (Jump to Subroutine) instruction.

In the SLC-500 operating system, only LAD2 is automatically executed when the controller powers up. Every other LADx program file has to be executed by a Jump to Subroutine (JSR) instruction or be triggered by a feature like a Discrete Input Interrupt or a Selectable Timed Interrupt.

Right-click on either the input or output address and select "Cross Reference" to look for duplicate address conflicts.

To easily find the JSR that refers to the LAD3 subroutine, type "U:3" in the Search field in the Standard Toolbar at the top of the RSLogix 500 window, and click the Find All button.

 

[Ramil.R]

Welcome to the PLCTalk forum community ! Are you really in Azerbaijan or was that an accident of alphabetization when you registered ?

I agree that the two most likely explanations are a duplicate address conflict or that LAD3 is not being called by a JSR (Jump to Subroutine) instruction.

In the SLC-500 operating system, only LAD2 is automatically executed when the controller powers up. Every other LADx program file has to be executed by a Jump to Subroutine (JSR) instruction or be triggered by a feature like a Discrete Input Interrupt or a Selectable Timed Interrupt.

Right-click on either the input or output address and select "Cross Reference" to look for duplicate address conflicts.

To easily find the JSR that refers to the LAD3 subroutine, type "U:3" in the Search field in the Standard Toolbar at the top of the RSLogix 500 window, and click the Find All button.

Thank you very much. I am new to this forum and happy about this. There is useful information. Thanks for being the creator of such kind of forum.
Yes, I am from Azerbaijan).
LAD3 is being called by a JSR instruction and in LAD3 only "Digital Link Input" instructions do not work properly but there is no problem with "digital input"

 

[Mickey]

Post your .RSS file if you can. Zip it first then post.

Someone may spot something in your program.

 

[Ken Roach]

Right-click on N18:10/0 ( or /1 or /2) and select Cross-Reference.

Do the same on B3:101/0 (or /1 or /2).

The most likely problem is something writing over those addresses. Maybe it's at the word or file level (like that MOV does on Rung 8) or bitwise in additional OTE or OTU instructions elsewhere in the program.

Check also for any "Temporary End" (TND) or "Return from Subroutine" (RET) instructions earlier in the LAD3 routine.

Ladder logic with XIC and OTE is about the simplest thing that a PLC does. If the program logic is being executed, and there is nothing writing over those same addresses, then they *must* work.