[sdiy] Reverse engineer an EPROM encoding?

[Gordon JC Pearce]

On Wed, Nov 13, 2013 at 12:46:15PM +0000, Jack Jackson wrote:
> Could anyone explain the topology/operation of the TR707?
> 
> I understand they have eproms that hold a few hundred samples of on sound sample. But what drives them? What is the output of the eeprom? and what is it fed into?

If it's anything like the 626 the ROM has an odd mapping (presumably to make laying out PCB traces easier).  The upper bits of the ROM are also used to map the outputs via a 4051 MUX.  The data lines of the mask-programmed ROM are fed to an R-2R ladder, then buffered and fed to the MUX.

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Gordonjcp MM0YEQ