Changing from Melsec A3H CPU to A3A CPU

hello all,

due to a crash of our old Melsec A3H CPU, I change it to a A3A CPU. I have convert my program to A3A with GX Developper. In the manual, they are compatible. When I run the program in the new cpu, disfonctionnements appears. It seems that A3A is too much fast for my program because in some case, we are doing set/reset on one bit in the same step or doing calculation by reading and charging the same word line after line and it doesn't execute all the instructions compare to the old cpu !!!
Has anybody had the same problem or is it something to do to make my program compatible to A3A ?

Thanks in advance

Hi Ptilou,

Differences in CPU and in GX compiler can both affect the way your initial program is computed.

From GX side : select one of your identified problems and compare IL codes for A3H and A3A. You can see the way your tags or data are translated from the "graph" layer to PLC codes, when converted from old to new CPU or not (you'll only read Mitsu functions and absolute addresses, even if you wrote IEC functions blocks or SFC i.e). You should see/understand why data you read/charge are not updated when you thought they were. Examine how single bits are used/written several times when they reflect intermediate variables. See if your software has "compiler options" where you can choose to refresh data each time it's called/loaded. See if you get "warnings" when compiling your program with data read/charged several times within one ladder or FBD network.

From PLC side : see in PLC configuration folders what kind of special register could affect the differences you met. If new and fast CPUs offer more adjustable functions, anyway they continue to scan their program the same way you experienced in the past - so what means "two much fast" ? (On the other hand, what pleasure if your japanese partner offers new products without new behaviors ? Imagine : they built some unpredictable internal monitor especially for you !). Download last versions of manuals and see if SET/RESET are executed the way you knew in all environments. Did you latch/unlatch bits through differential trailing/leading edges ? in what kind of programming environment (SFC step, ladder...) ? Did you latch variable tags or I/O in absolute address ? Keep in mind when answering that your PLC executes codes tranlated from graph to IL by the GX compiler !

Hope this helps.

The short answer is "YES", I met many cases like that. Detailed answers... could be very complex - but interesting - since GX initially was (is today ?) based on a Softing product, with an original platform common to several brands (i.e see SoftControl for OEM at http://www.softing.com). What says the Help/About section in GX ?

Laurent

Can you explain in more detail steps you did during conversion?
Are you sure you transfered data tables as well (not just logic)?

Hi,

Thanks to Laurent for his fast reply.
Today, I receive a mail from Mitsubishi Japan. In fact, they write in mail that programmings are different between A3H and A3A (strange because A3A is sold for a compatible CPU for A3H) and also, speed counter module AD61 we have in our racks are not compatible with new CPU. They'll make themself modifications in my program because it seems that it's too much complicated to do by a newbie like me
When I'll receive more information, I'll explain it in some words here

Have a good day

Ptilou