SLC 504 OS versions

Could someone explain the SLC 504 OS versions, series A to E or firmware? I have an old SLC504 that says it is an OS401. This CPU seems to be older than Google searches where used hardware is showing up as series A to E. Do the newer versions just have bug fixes and some new instructions? Can I use RSlogix to read my firmware version?

AFAIK, OS401 is the latest version and came in series A, B or C, with C being the most recent. Each series then had different firmware revision numbers (FRN) with FRN 11 (I think) being the latest in November 2012. You can get a kit to upgrade the processor as described here but I’m not sure how recent your processor must be to upgrade it to the newest firmware.

Have a look at this release note for information on the kind of things fixed.

I think you also have to match your version of RSLogix 500 to the version of controller firmware, but I don’t know whether you can use it to read the firmware version or not.

thank you