The 6502 Lives!!
The SPLB20D2 CPU mentioned in the MSNBC article (there's a link in a forum entry a dozen or so lines below this) is in fact a Sunplus CPU - they call it an LCD controller for data bank.
See this chip & related ones at
http://w3.sunplus.com.tw/products/lcdcontroller/splb.htm
While these data sheets give the specifications for hardware, I/O and memory layout they don't indicate overall CPU architecture other than calling it an "8-bit RISC processor". There's another document around somewhere else that'll go into register layout, opcodes, etc.
From prior searches about Sunplus, I'm pretty sure this is a 6502-based CPU. (Their other low-end 8bit CPU is an 8051, but I think this just shows up as a core in other special function ASIC products like their camera/imaging/speech chips.) A brief look indicates it has 32KB ROM and ?? RAM (I believe this is purchaser-selectable, since RAM takes up a fair bit of die area and thus affects the cost.)
The memory map indicates some vectors in the $FFF0 region, which is consistent w/6502 architecture. (A standard 6502 has 2-byte vector entries for /RST, /IRQ and /NMI in the upper 6 bytes of its 64KB addr space. Peripherals may add some extra interrupt vectors to this design.)
I am not yet sure if this is a plain 6502 instruction set or a improved 65C02 instruction set - or some crazy mix of the two.
This looks to be a ROM'd chip - as opposed to flash or EPROM - and there may not be a way to dump/verify ROM data for reverse engineering.
There is a good chance that much of the HP12C-Plat ROM code is written in C not assembly - making reverse engineering harder. (It can be easier to figure what another engineer does, except when he gets real 'tricky', than to guess what a compiler does.)
In a perfect world, if this were in a PLCC package like orig 12C and there were spare lines for address & data we could just clamp on an EPROM on top, put the chip into emulation mode and have fun. Guess not.
When I know more I will let y'all know... maybe there's room for hacking...
Hope so, as I love the 6502. Been a long time since my Commodore 64 days!
Bill Wiese
San Jose, CA
bill[at]bwiese[dot]org