It appears the EDC15M is a OTP-style chip arrangement too. Might be similar!
Waiting for another ECU so I can make a schematic, and check what the pins on the SCL4410-v4 go to. A hunch and some searching hints me toward it being an 80515 or something, either to merge the odd/even binaries before the C16x processor can use it, but unsure. Possibly someone with MSA15 knowledge knows how they work.
Dude this ECU has nothing to do with EDC15. Nip that shit in the bud.
Just because it uses similar automotive processor of the era does not mean anything.
Stop repeating this ridiculous assumption.
CPU can be a 80C196 variant or something completely different. I did not look at the code.
Also your 256k merged file - post the separate files as well. Did you just add them one after another or interleave the odd and even bytes?
If it's odd/even then it's 100% not a 8051 (80C515/80C535) variant, they can't read 16 bit, reads are 8 bit only.