That is NOT a PLC as commonly understood. It can not handle ladder logic. Is that mandatory ?

Not for using it, but for selling it as part of user programmable equipment to a typical PLC using factory.

If you program it yourself and use it as 'firmware', you can, of course, use anything.

However, whet is referred to in the industry as a "PLC" is ladder logic programmeble.

Just visualize what succes you would have selling something that was user programmable in forth.

Erik

as an anecdote, I got the job working with PLCs by mistake, at the interview I stated that I had years of experience with PLCs (programable Logic Chips).
So I had to learn ladder logic in a hurry.