Not a super important question, but I was wondering if anyone has ever known a 65C02 to boot without any RAM present? Mine won't and my guess is that it needs page 1 ($0100-$01FF) for the stack and utilises it during it's boot/reset sequence.

Just wondering.

I can't think of any reason why you can't boot a 6502/65C02 without RAM. It's a bit more difficult to initialize and operate a 6502/65C02 system without using subroutines, interrupts or traps (BRK). However, it would be very limiting, but still possible.

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Michael A.

IIRC, if your ROM has any JSR/RTS's it will need the stack.

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65Org16:https://github.com/ElEctric-EyE/verilog-6502

The 65C02 (or any other 6502 chip), as a chip, will happily run without RAM: the simplest example is the NOP tester, where you tie off the address bus with resistors to read EA. Many other values would also work: the chip will fetch instructions and execute them, and the address bus will act as a counter.

But any computer with a 65C02 in it (or any other 6502 family chip) will most likely not run well without RAM, because, as noted, it is very likely indeed to try to read back values previously written to zero page or to the stack, and without RAM it won't read the values expected.

What are you trying?

Remember the 6532 or RIOT (RAM IO Timer). It was the solution in the early days to allow building an SBC with minimal chip count and still have 128 bytes of RAM for a small stack and some page zero locations. Projects like the EMUF used it in conjunction with a 6504 and a 1k EPROM.

http://retro.hansotten.nl/index.php?page=emuf-6504

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6502 sources on GitHub: https://github.com/Klaus2m5