Help understanding H1, H2, H3 and IL instructions in Omron Sysmac S6

[Brunofunchas]

Hello everyone,

I’m currently working on upgrading an old Omron Sysmac S6 PLC program.

While reviewing the ladder logic, I came across references to H1, H2, and H3. I couldn’t find any explanation for these in the manual. From what I understand, they seem to be internal relay bits — can anyone confirm this?

Also, I noticed the program uses IL (Instruction List). I’m not very experienced with older Omron systems, but I believe it’s possible to use a Master Control Relay (MCR) for structuring conditional logic in IL. Is that correct?

Any clarification or documentation links would be greatly appreciated.

Thanks in advance,

Bruno

PLC - Rotativa.pdf

[IO_Rack]

44 minutes ago, Brunofunchas said:

I’m currently working on upgrading an old Omron Sysmac S6 PLC program.

Good move!

 

44 minutes ago, Brunofunchas said:

While reviewing the ladder logic, I came across references to H1, H2, and H3. I couldn’t find any explanation for these in the manual. From what I understand, they seem to be internal relay bits — can anyone confirm this?

That is correct. They are Holding Relays. They will retain their status on a power cycle. You didn't mention the PLC you are converting it to. If it's an Omron, the 'H' memory will be the same. The only difference with newer Omron PLCs is, the H bit will be reference by WORD first, then BIT. (H0.01 for example).

 

48 minutes ago, Brunofunchas said:

Also, I noticed the program uses IL (Instruction List). I’m not very experienced with older Omron systems, but I believe it’s possible to use a Master Control Relay (MCR) for structuring conditional logic in IL. Is that correct?

That is also correct. If the bit driving [IL] is NOT ON, then code between [IL] and [ILEND] will not be executed. I will have to confirm the behavior of the outputs in between, when execution is turned OFF. Omron has different instructions for different behavior. I'll post back with details.

[Brunofunchas]

Thanks IO_Rack for the reply.

The PLC will be an OMRON NX1P2-9024DT1.

[IO_Rack]

5 minutes ago, Brunofunchas said:

The PLC will be an OMRON NX1P2-9024DT1.

In that case, you will want to check the "Retain" box for the H bit variable replacements. 

[Brunofunchas]

1 minute ago, IO_Rack said:

In that case, you will want to check the "Retain" box for the H bit variable replacements. 

Thanks again.

[Brunofunchas]

I'm confused with the program, because I can't see where it writes to H0 up to H4. Are they related to KR latching relays?

Edited April 30 by Brunofunchas

[IO_Rack]

Quite honestly, I don't remember.

This site was overhauled a few times over the years and files became corrupt. Here is another broken link that I will report to @Chris Elston. He can fix the links but it won't be immediately. 

https://mrplc.com/files/file/56-omron-sysmac-s6-programmable-controller-operation-manual/

 

In an attempt to answer your question, I have researched some of our old programs but even those are beyond our data retention policy, so they are gone. I haven't found a reliable download for this manual either. 

I've browsed your program. Using some deductive reasoning, I would say the KR instructions are related to the H memory. For example, "1" would refer to physical input 1, so it wouldn't have an output in the program. I would think the KR1 would refer to H1 since I don't see any other 1s in the program. Timers and Counter are obvious.

Ultimately, I would test this, but I don't have a means of doing so.

 

Edited May 2 by IO_Rack
My guess was wrong. See chelton's answer below.

[chelton]

Although it doesn't show in the manual I would think the H1..31 would be outputs of the hight speed counter HDM instruction just as R1..xx would be outputs of the reversible counter RDM instruction.

There's a scanned manual on scribd. Google search for W010E32.

[Brunofunchas]

12 hours ago, chelton said:

Although it doesn't show in the manual I would think the H1..31 would be outputs of the hight speed counter HDM instruction just as R1..xx would be outputs of the reversible counter RDM instruction.

There's a scanned manual on scribd. Google search for W010E32.

You’re absolutely right! While digging through the machine’s documentation, I came across a paper that confirms the conclusion you mentioned. It specifies preset values for HDM00 to HDM05 and RDM00 to RDM02. With the exception of H5, these match the variables used in the program, which suggests we’re on the right track. Although H5 isn’t used directly in the program, the document indicates it functions as the reset for the HDM. So, I’ll wire it to the reset input of the HDM on the new PLC.

RS2510 - Internal Variables Settings.pdf

[chelton]

Your lucky to have such detailed schematics. Good luck with the upgrade.

[Chris Elston]

On 5/1/2025 at 7:32 AM, IO_Rack said:

Quite honestly, I don't remember.

This site was overhauled a few times over the years and files became corrupt. Here is another broken link that I will report to @Chris Elston. He can fix the links but it won't be immediately. 

https://mrplc.com/files/file/56-omron-sysmac-s6-programmable-controller-operation-manual/

 

 

This file is fixed as well now.

[Brunofunchas]

On 5/2/2025 at 8:29 PM, chelton said:

Your lucky to have such detailed schematics. Good luck with the upgrade.

Thanks! I have confirmed with OMRON official support that H0…H.. refers to the outputs of the HDM, and the R’s are for the RDM. I will migrate the instruction to a CTUD instruction.