Inspired by renewed discussions about overclocking, I think a producible (in hobbyist quantity) very fast 6502 computer may be an interesting exercise in PC board design rules and CPU testing--and also the bragging right of having a really fast, if not the fastest, production 6502 computer.
29.5MHz 6502 is already a reality, so I want to go faster by prototyping a stacked W65C02 computer that minimizes wire length and uses faster components. I'm shooting for low 30MHz operation with the prototype. With proper PCB design, I think it can run faster than prototype so if I can achieve low-to-mid-30MHz operation with a prototype, perhaps a functional W65C02 computer can run to near 40MHz.
The design is based on
CRC65 which has very few components and has demonstrated to run to 29,.5MHz reliably. To make it run even faster:
* minimize wire length and circuit loading, thus
- 3D stacking
- no parallel expansion bus
* fast 10nS RAM
* fast DOM drive
* Buffer clock through CPLD
* larger CPLD, not necessarily for speed consideration but to simplify interconnect.
Picture show the components I plan to use, and how they'll be put together. The CPLD board is the base, W65C02 in PLCC44 package is in the middle of stack and 10nS RAM is on top. 6502 has fixed pin assignments, but RAM and CPLD's signal assignments are flexible which is important to achieve short point-to-point interconnects. This should be a functioning computer with mass storage and capable of running DOS/65
Even with short point-to-point interconnect, I expect this to be a messy ball of wires!
Bill
PS, I'll publish a schematic next post, but for the assembler, namely yours truly, it is the construction guide that need particular careful consideration.