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. Or at least copy the code into RAM.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 it talks about is saving/loading the code from tape, which I dont have, just ROMs.
I am trying to get the Host link adapter, as using the load/save method seems to be very hit and miss, mostly miss.I appreciate any help or suggestions.Thanks.
The plan is to eventually replace these with a newer PLC, but for the time being I have to keep these going.
