This made me wonder if anyone had designed a 64-but 6502. Came across this http://www.6502.org/users/andre/adv65/index.html which in turn links to many different things including a project that they had started on with making a 64-bit extension to 6502 for fun.

There is too much TimeCube on that WWW site. Try this one.

* https://retrocomputing.stackexchange.com/questions/14864/wha...

From skimming the datasheet, it looks like a fairly bad product. Sure the A register is extended to 32 bits, but the 8 bit data bus means that it's not going to be much faster than the 65816 and the address bus is still 24 bits. I have no clue why WDC decided to keep the same pinout as the 65816.

> I have no clue why WDC decided to keep the same pinout as the 65816.

The entire market for this new chip would have been 100% of the people with a 65816 and only those people. Companies do this for a couple reasons, last ditch effort to get cash flow or bridge a gap in a delayed product, extend a product line another cycle, etc.

Pinouts are powerful interfaces (semantically), look at the op-amp, what a wonderful design.

*edit, turns out this chip would have gone in last model of the Apple IIGS but it was the 65816 instead.

I find this stuff fascinating, how technologies fold and morph over time. Esp with MIPS pivoting into RISC-V.

Oh, it even has a datasheet! Thanks, that's amazing! The missing SEV instruction could have been aliased to SEP #$40. The only thing missing to produce a working replica today (in hardware or software, just for fun of course,) was indeed the XFE designation. The only place it could have gone was in the WDM prefix, but it could have been any byte after that. We would have to outright guess. He couldn't have reused XCE for it without risking perfect backward-compatibility (though of course he may have decided to do that anyway.)