NEC uPD1771C Notes

What is this?

This repository is a collection of notes and a disassembly (and disassembler written in C) of the firmwares 11 and 17 for documentation purposes.

What is the 1771?

An 8-bit microcontroller, with the main focus of generating sound. It cannot be reprogrammed but can have its mask ROM dumped.

What is this used in?

For now there are two devices in this repository, the Epoch Super Cassette Vision, a rather obscure japanese console released around in the same time as the Famicom and the Grandstand Firefox F-7, a tabletop VFD game. It is also used on the NEC APC, but that firmware has not been dumped yet.

Many thanks to

• PLGDavid for dumping the ROMs and sharing them with me.
• Oura Oguchi for making the 1771 documentation and schematics on his website - https://oura.oguchi-rd.com
• A few friends, namely kagamiin for showing me what an ADPCM decoder should look like, Lockster for showing a document that had a few guesses and observations based on Star Speeder and Colton and Axiom for teaching me how to use the C Standard Library file printing functions used for the disassembler.
• ReverendGumby on the NESdev discord for sharing some useful information about some weird behaviours such as opcode $FFFF and N timer below the TONE4 range

But why?

For science! And hey this should hopefully help out with emulation.