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ricard 15th Oct 2011 10:22 pm

NEC µPD78312 opcode map anyone?
Ok, so this is sligthly off-topic as it is not related to a vintage computer as such, but it is related to mid-80's microcontroller technology, so I'm giving it a shot:

I'm trying to disassemble a ROM for a system (a Roland D-50 synthesiser if you must) that contains a NEC µPD78312 microcontroller. Initially, I thought it was the same opcodes as for the µPD7812, for whom I found both a disassembler and complete data sheet on the 'net. But after disassembling the code it appears the opcodes (and possibly the instruction set too; I haven't checked in detail) are different. Although there are several links to µPD78312 datasheets on the 'net too, none of them actually list the actual opcodes used (although in some there are tables of what the various machine language instructions do, cycle timings etc, but no actual opcode maps). And I haven't found a disassmbler either.

So I'm wondering if anyone here would have some documentation for the 78312 which they could share, such as scanning a page with the opcode map from a processor user manual, or something similar. [Source code for] a disassembler would be even nicer, but probably even more rare.

frsimen 16th Oct 2011 3:34 pm

Re: NEC µPD78312 opcode map anyone?

The 57 page data at this site:
gives the binary value of each of the opcodes. It's a bit of a chore, but from that you can draw up your own table of opcodes. A lot of the instructions seem to use two op codes, just to add to add to the fun.


ricard 16th Oct 2011 8:06 pm

Re: NEC µPD78312 opcode map anyone?
Thanks a million, that's just what I've been looking for!

I guess I should have continued to search, I gave up after a couple attempts which seemed to indicate there were basically two different data sheets in the archives, none of which listed the actual opcodes.

Agreed, it's a bit of a chore to put together a complete opcode map, but in my specific case I only need a couple of opcodes so this will do fine.

ricard 17th Oct 2011 10:53 pm

Re: NEC µPD78312 opcode map anyone?
Just for completeness: further investigations told me that the µPD78312 is a member of the NEC 78K/III family, of which the µPD78322 is also a member.

That in turn led me to , which has a downloadable 78K/III disassmbler. Appearently it is only a demo version, allowing at the most a code size of 8 kbytes, but there's nothing stopping you from splitting the input file into 8k segments and disassembling them one at a time.

Seems to work under Linux using Wine too.

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