In article <1gg1isg.1a35pyatdcuq8N%dempson@actrix.gen.nz>,
David Empson <dempson@actrix.gen.nz> wrote:
Paul Schlyter <pausch@saaf.se> wrote:
In article <20040625200651094+1200@News.Individual.NET>,
Roger Johnstone <rojaws@orcon.net.nz> wrote:
ProDOS technical note #23 says:
ProDOS 8 1.3
Warning: This is not a stable version of ProDOS due to an
illegal 65C02 instruction which was added. This version can
damage disks if used with a 6502 processor.
http://web.pdx.edu/~heiss/technotes/pdos/tn.pdos.23.html
I take it to mean that it was a valid 65C02 but invalid 6502 instruction,
The text said "illegal 65C02 instruction". And since the 65C02 was
backwards compatible with the 6502 at the machine code level, it was
definitely an illegal 6502 operation as well.
The technical note was badly worded. They didn't use an "illegal 65C02
instruction". It should have said that they "illegally used a 65C02
instruction".
Even that is bad wording: there's nothing "illegal" in using opcodes in
a new processor which was unavailable in older processors. After all
these new opcodes are there to be used, right?
A better wording would be: "used a 65C02 instruction not backwards
compatible with the 6502". Yes, this phrase is a bit longer, but it
does tell well what actually happened.