A-B 5/40 Series E Scan Time vs. Series A

I recently replaced one of our PLC5/40 series A processors with a series E, and noticed that scan time was reduced by about 25%. I saw that the release notes for the series C processor included "Enhanced execution times for some instructions." I emailed Rockwell asking if they could tell me which instructions were enhanced, and by how much.

The response back was that they did not perform these sorts of timing tests, but assuming the instructions were performed in the FW rather than the custom ASIC,it would probably be in the tens of microseconds.

Since I can't get specific information on improved scan times with the series C and later, I was wondering if anyone here has experience with this type of harware change. Are my scan time improvements typical for this kind of change? Has anyone performed this type of change and not see an improvement?

Your improvement in scan time is entirely possible but not necessarily probable. I replaced a PLC5 three years ago and noticed a faster scan time as well. I didn't pursue why, I just carried on knowing about the benefit. I attributed the faster time to AB improving the platform's processor.

As far as I know newer revisions of PLC5 hardware based on newer and faster processors.
Instruction execution time, housekeeping and overhead is faster.