Re: 65c816 in a IIc

[David Wilson <mcs6502@gmail.com>]

On Apr 20, 1:49 pm, gids...@sasktel.net wrote:
> On Apr 19, 8:28 pm, A2Aviator <a2avia...@gmail.com> wrote:
>
> > Yes, I have put them in directly on the motherboard. You get a 65802.
> > If you wanna run Merlin 816 you can. The enabling of one pin make the
> > 16 bit come alive, but otherwise it's just an '802 when it's inserted
> > on an 8 bit motherboard.
>
> Now you gone and done it.  You opened a whole can of worms there.  :)
>
> Which pin do you enable?

There isn't a pin as such. The 65802 is pin compatible with the 6502
[see page 544 of Programming the 65816 by David Eyes/Ron Lichty]. The
65816 has a number of pins that differ:

pin = 6502 -> 65816
1 = Vss -> /VP (output)
3 = phi1 (output) -> /ABORT (input)
5 = NC -> /ML (output)
7 = SYNC (output) -> VPA (output)
35 = NC -> E (output)
36 = NC -> BE (input)
38 = /SO (input) -> M/X (output)
39 = phi2 (output) -> VDA (output)

In addition the extra 8 address bits are output on the Data Bus during
Phi1. By plugging a 65816 into a 6502/65c02 socket you are shorting /
VP to ground and leaving a number of other signals potentially
undefined.

When using a 65802 (or a 65816 in a suitably configured socket) in a
16 bit address bus environment the bank bytes are simply ignored - all
the banks are the same.
> How does it work with the mnemonics that have 4-byte addressing modes
> since the 4th byte of these mnemonis refer to a bank number?
> Doesn't Merlin 816 rely on GSOS to load and save files or use the ROM
> tools built into a IIGS to be able to run?
> Would you happen to have a list of programs that can run in 16 bit
> mode on a IIc?
>
> Or better yet.  Do you have a cool website that explains all and gives
> the answers to my questions?
>
> Oh, how I yearn for your knowledge.   :))))
>
> Rob