Omron Sysmac C20 ROM usage

clemm

Member
Join Date
Feb 2018
Location
Perth
Posts
3
Hi,

I have taken over maintaining some HVAC units that are run by the Sysmac C20 PLC.

To keep a stock of PLCs handy we have had to buy used PLCs from Ebay.
The current PLCs are fitted with ROMs that I presume contain the ladder code in them. I have managed to just fit the OS and data ROMs into these 'new' PLCs and about 45% of the time they work.
To try to work out how it all works, I removed the ROM and cleared the RAM contents, using the programming module, so that I can write some basic testing code to test the PLCs and make sure the relays are good in the 'new' PLCs.
After playing around I cleared the RAM again, then replaced the original code ROM and set the DIP switches to the ROM setting. On switch on, the unit does not appear to be working, checking the code using the programming module I see no code.

To try and figure out whats going on, I removed the ROM from a working PLC and the unit still works, which I guess means the code is running in RAM.
I had assumed that setting the DIP switches would make the code run from ROM. Is there something I am missing?
Is there some action I need to do to get the ROM code copied into RAM?
The manual doesn't really expand on using ROMs.
All is talks about is saving/loading the code from tape, which I dont have, just ROMs.

I appreciate any help or suggestions.

Thanks.
 
1st of all, I don't remember much about these units. There is a way to get around having an old data tape recorder. There is some sound recording software by Audacity that can be used to make a .wav file. You would need a handheld programmer with a tape input/output jack on it and a computer with a sound card. Then you need an audio patch cord to connect between the two.
I have done this on some other brands of plcs simply because I couldn't find any tape type recorders available.

There may also be some software available to program with so you won't need to write the code with a handheld programmer, It would just be needed for the data/audio cable connection.
 
Last edited:
Thanks for the suggestion, I had been mulling that idea over as a last resort, but sounds like it will be the first resort.
 
This is going way back.

The C20 is supported by Syswin software. No longer supported by Omron and you will need to use Windows XP OS.

You will also need a Host Link unit # 3G2C7-LK201, also no longer available from Omron.

You may be able to locate both on ebay.

Honestly, I would strongly suggest you work on replacing the C20 units with current hardware. The C**K units were discontinued in 2002 and the C20 was some years before that.

Good Luck.
 
If I remember correctly I think the ROM transfers to RAM to run but I have not seen one of these since about 1992! It may be worth putting this on mrplc.com - there are some older Omron techos over there that will probably know straight away. Should heve been replaced many years ago.
 
Thanks for all the suggestions.

One of the ongoing plans is to replace these old C20's as it is getting hard to find replacements.
I have requested that we purchase the Host link adapter, so its hurry up and wait for now.

I will post in the MrPLC forum and see if I get anywhere from there.
I just wish that there was some form of IO map for the C20 or some more detailed information so I could understand how the RAM and ROM work together.
I had assumed that the ROM would be copied to the RAM but I have not seen that happen on the majority of the C20's I have.
And there is no mention of it in the manual, or even any details on how to force it, if at all.
So if you can only copy the code into it via the host link adapter or via an audio interface, whats the point of having ROM?

So many questions.....
Anyway thanks again for the advice.
 
I think it does copy from EPROM to RAM but cannot remember. I can still remember using the hand held, EPROM writer, printer interface but that is all. If I had one stuck in front of me now I would not know what to do! With the host link unit I can remember using the old CAPS DOS software - so long ago. I would have been replacing these back in the very early 2000s.
 
I did not use the C20, but have used many C**K units.

From what I remember, you could have two different programs in those units. One in RAM and one on ROM. Changing the DIP switches determined which program would execute.

The documentation on the C20 is sparse. That was typical of manuals of that time period.

The Host Link will have a DB25 pin female connector. You will need a null modem cable to your computer.
 
gclshortt +1

Least intuitive software I have ever used.

DOS Caps software BobB referred to has been gone for years.

Syswin was pretty decent. Just checked, there is Syswin on ebay.
Syswin will need to be run in Windows XP.
 

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