Re: wanted:info on IIe extension

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <35m4hf$bor@maxwell4.ee> dpscholn@mtu.edu (Dan P. Scholnik) writes:
>	Well, I found a cross assembler that lists the instruction set for
>the 6502, 65c02, and the 65c00/21 (whatever that is) . It claims that the
>65c02 has instructions BBR0 throught BBR7, and several other bit-test
>instructions. BBR is Branch on Bit Reset. I have not seen these anywhere else
>and so I wonder if this assembler just got mixed up as to what was from
>which processor......

Apparently there is (or was) more than one version of the 65C02.  Some
versions (Rockwell's in particular) have the extra BBR0-7, BBS0-7, RMB0-7
("Reset Memory Bit") and SMB0-7 ("Set Memory Bit") instructions.  These
instructions are missing in the versions used in Apple II's.

I was interested to discover that the MM50740 (the 6502-based processor
used as the Apple Desktop Bus controller in the IIGS) has these
instructions.  It's not really like a Rockwell 65C02, though, since it's
missing several other 65C02 opcodes, and it has several new instructions
and addressing modes not found in any 65C02.

               - Neil Parker
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