Re: 65c02 in ][+ problem

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

John L <jd@logotech.8m.com> wrote:

> I've got a Rockwell 65c02 CPU running quite well in my ][+ (64K with
> language card), however, I can't seem to get ProDOS 2.0.3 running at
> all.  When I attempt to boot P8 2.0.3 from any device I get the splash
> screen then the system locks up with a few garbage characters.  

One possible explanation is that ProDOS is trying to use a CPU detection
algorithm which involves 65802/65816 instructions but doesn't allow for
the Rockwell R65C02.

The R65C02 defines unique instructions for all opcodes with low order
four bits of '3', '7', 'B' or 'F'.  These intructions are reserved on
standard 65C02 (they are guaranteed to be NOP), and have completely
different functions on the 65802/65816.

(On the original 6502, all undefined opcodes are reserved and have
behaviour which is not documented officially, which is typically a
mixture of other related instructions.)

Has anyone else had P8 2.x running successfully on a II+ with replaced
CPU?  If so, what CPU was involved?

I suspect that P8 2.x will work fine in a II+ if a 65802 or Zip chip is
used.  Most (all?) non-Rockwell 65C02s don't work at all in a II+, due
to timing or electrical signal problems.

> I thought perhaps the lockup was due to P8 2.0.3 requiring the //e
> mousetext ROMs - further investigating reveals this not to be (A 65c02
> CPU is the only requirement).

There is no possibility that any software would fail to operate based on
the character set available in the video ROMs - these ROMs are not
accessible to software, and only affect the appearance of data on the
screen.  The lack (or availability) of MouseText could cause a program
to be difficult or impossible to use due to the screen display showing
the wrong character set.

The IIe firmware might have been a requirement, but I don't think that
is the case with P8 2.x.