Mitsubishi PLC Scan Sequence

I know that an Allen-Bradley PLC will scan every input first and store them in memory, then solve the ladder, then update the outputs. I'm wondering if EVERY PLC follows this same sequence, specifically a Mitsubishi PLC? My coworkers seem to believe that a Mitsubishi PLC scans rung for rung instead.

As a standard template you can say that within a PLC scan sequence the order is usuually first update your input data tables, then execute your program from top to bottom left to right, then update your output data tables, then loop back and do it again and again. To really answer your question i would look up the manual for the specific PLC you are using and read up on how the scans execute, because some brands can differ from others. An example of this is the Logix 5000 based PLC that allen bradely supportt. In that instance you can have your input data update midway through the scan sequence, and to avoid that you incorporate a buffer to that tag etc. As far as what your coworkers said "a Mitsubishi PLC scans rung for rung instead" that is a very vague way to put it, look up the manual.

any PLC does rung scans for all the inputs and markers (when you set a marker in a rung above you can use it in the rung below, and yes you can change inputs in memory, however all inputs are first transfered into memory (as markers) and at the end of the cycle all outputs are set according to the outputmarkers)
For an output it is easy to check:
rung 1 set output1
rung 2 reset output1
run program if output1 is on they are correct if nothing happens you are correct.
inputs can not be done this way as program is too fast .

Keep in mind that with mitsubishi you can have several task pools and that execution control can be event based, interval based and priority based.

Best regards,
Vuckovic Goran.