Re: 65c02 in ][+ problem

[John L <jd@logotech.8m.com>]

On Tue, 4 Dec 2001 12:26:27 +1300, dempson@actrix.gen.nz (David
Empson) wrote:

>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.

How compatible is the R65c02 with the 8-bit mode of the 65816 ?

Assuming this CPU detection algorithm is correct, how is it that an
enhanced //e running an R65c02 can run P8 2.0.3 without trouble ?

Perhaps P8 2.0.3 also looks for //e firmware in addition to the CPU
detection ?
 
>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.

I knew there were some differences between the R65c02 and other 65c02
variants, but from what I've researched, the differences are not
normally visible unless one fails to comply with correct progamming
guidelines.  I've noticed some copy protected games fail to run
properly on my ][+ with the R65c02.

>(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.

The Rockwell 65c02 I'm using actually came from a TransWarp
accelerator card which failed to work on my //e.  The CPU is
operational and is rated at 4MHz.  Interestingly, I could never get
the TransWarp  to work at all on my //e yet it worked occasionally on
my ][+.  Every time I tried to operate the TW on the //e, I got a
screen full of "@" characters.

Thanks for your help, David.  I might try getting my TransWarp
operational again although it might be a problem since the firmware
seems to be corrupt.  The startup "TransWarp" logo is all shaky at
startup and the sceen display is unstable when I use it on a ][+.




John