Re: Apple IIe / ProDOS / Y2K?

[Randy Shackelford <shack@onyx.southwind.net>]

Liam Busey <liam1@ix.netcom.com> wrote:

:>> I replaced the 6502 with a 65802 a long time ago, it's a better >> replacement chip than the 65C02.
:> 
:> What is a 65802 and why is it better? Is it a replacement for the
:> 65C02 in my Apple //e enhanced?

: The 65802 is basically a 65816 that was crippled to be pin compatible
: with a 6502 or 65c02. If one were to plug in a 65802 into the CPU socket
: of their 8 bit Apple II they'd have access to all the increased
: functionality of the 16 bit 65816 but only the 64k address space of a
: 6502 (65816 can address 16Mb). In reality the 65802 isn't much of an
: upgrade because very little software supports it's 16 bit mode.

It's more accurate to say a 65802 is a 65816 in a 6502 pin compatible
package. All the 65816 addressing modes and instructions are there, the
only thing is the bank select registers etc have no connection and hence
have no effect.

Like anything else, there needs to be software to utilize hardware or else
it isn't much use. Glen Bredon seemed to be the champion of software support
for hybrid 16 bit boxes. His Merlin assembler as well as parts of Prosel
8 could utilize a 65802.

Since the 65802 fixed the bugs in the 6502 e.g. the indirect JMP crossing
a page boundary bug with no changes to the cycle counts for the affected
instructions, it is considered a better 6502 replacement than the 65C02.
Plus you get the added instructions and addressing modes for your trouble.

I recall seeing someone say a long time ago that they swapped a spare 65816
directly into a //e and it worked. The main pin differences involve how
the bank address pins are multiplexed with the data I/O pins, and the
vector pull and abort pins as well. That's what I remember without my
Programming the 65816 book handy. It could be that the 65816 happens to work,
although I've never tried to duplicate what I read myself. I have a perfectly
good 65802 in my //e already.

I got it just over ten years ago. I tried to buy one and couldn't find a
place which would sell me one, so one company sent me a free sample. I think
WDC et al quit making them several years ago.
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