Hello. I'm completely new to the world of 6502 (and its derivatives, in this case).

I got interesting in dumping the ROM from this Mitsubishi M38258MCM166FP microcontroller that I found in a guitar multi-FX unit (Korg AX1500G). There's no obvious ROM interface or separate ROM chip so I thought I'd have a shot at using clock fault-injection to make the chip dump itself. It was labourious but I did manage to get everything out. Here's a nice diagram of the address space from the datasheet:



Just before the user ROM, there is a reserved area. The datasheet says this:



Those two bytes read thusly:


I opened up the reserved ROM in IDA. It fits into 128 bytes perfectly.

http://forum.6502.org/download/file.php?mode=view&id=9080
(huge image so I decided to link it)

Any guesses as to what it does (out of curiosity)?
FYI the 740 Family instruction set is a bit larger than 6502 so I enabled IDA's auto comments to describe every instruction.

Here's a readout in text, in the case that you prefer that:
https://pastebin.com/0LNY7r7r

Welcome -- and nice hacking!

As for what the thing does, I'm guessing this is one of the older effects pedals that use analog technology for most or all of the actual signal processing, but there's a microcontroller in charge, tweaking the analog control signals and providing the user interface. (The newer gear simply uses Digital Signal Processing.)

Are you a jammer as well as a hacker? There are a few of us on this forum...

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Hi Jeff


Thanks. It's a bit of a time sink but it's enjoyable.



I didn't know that there even are analog multi-FX pedals. This one is very digital but fairly early - about 1995. It uses the same DSP from the original Line6 POD and Digitech Whammy XP-100.

The ROM is big - 48KiB. 34 of that is in use with all the FX logic and DSP programs+data. The bit I was curious about it this testing ROM, specifically for testing the MCU and probably not the whole unit. It does some weird things (like setting decimal and transfer mode and then immediately clearing them).



Yes I'm a jammer. Only low frequency though
Occasionally I post YT videos about FX pedals or audio hacks, among other trash You can check out my channel, but don't feel obliged.