Re: Apple /// processor

[reid@hplvec.LVLD.HP.COM (Reid Trimble)]

In comp.sys.apple2, dempson@swell.actrix.gen.nz (David Empson) writes:

    > The main advantages of the 'C02 are the new instructions and the fact
    > that it is CMOS, which reduces the power consumption.

Probably the only real advantage is power consumption.  There isn't any
simple way to take advantage of the new instructions or addressing modes
unless you are willing to write your own assembler or try to fake them in
with macros.

    > I can't say whether or not a 65C02 would work in an Apple ///.  

It should work just fine.  The /// did not suffer from the odd bus timing of
the early ][ 's.

    > I suspect that it won't work very well - the Apple /// have special
    > hardware to extend certain addressing modes to support more than 64k,
    > and this hardware is unlikely to work with new 65C02 instructions.
    > Does the /// redefine (or add) any opcodes to the standard 6502 set?
    > If so, the 65C02 is unlikely to work.

All the special Apple /// features are accessed through a 4 byte code sequence
that begins with the BRK instruction.  New or redefined op-codes have no
affect on this architecture and in fact co-exist just fine.  As I mentioned
earlier, the only problem you face is actually getting a program you write
to call the new instructions unless you hand code them in hex!