Re: Can an apple II take a C64 microprocessor?

[dempson@actrix.gen.nz (David Empson)]

Mike Westerfield <MikeW50@aol.com> wrote:

> You can safely put in the 65c02 or the much more powerful 65802 (assuming
> you can find one). While the Apple //e upgrade for the 65c02 came with some
> ROMs, the upgrade of the chip and ROMs were entirely separate affairs. You
> can definitely use the 65c02 without installing the new ROMs. (I'm not sure
> if the reverse is true, though.)

It is safe to do either combination.  The enhanced IIe firmware was
deliberately written to avoid the use of 65C02 instructions, so that you
could mix new or old firmware with either processor.

Whether it is a good idea to do this is another question.  Most software
looks at the firmware to identify whether the machine is enhanced.  If
you have the enhanced firmware and a 6502 processor, the software may
assume it is safe to use 65C02 instructions, which is likely to cause
weird problems.

> There was a Rockwell chip whose number escapes me that can also be used;

It was just Rockwell's variant of the 65C02 (the R65C02).  It includes a
series of bit-manipulation instructions (e.g. set or reset a single bit
in a zero page location) in the $x3, $x7, $xB and $xF columns of the
opcode map (64 opcodes in total).

All Rockwell 65C02 chips have these extra instructions (they don't make
one without them).  They are most useful in embedded programming if you
have I/O peripherals mapped into memory in the zero page area.

Note that none of these instructions are compatible with the 65802 or
65816, or a 6502 or 65C02 from any other manufacturer.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand