Re: WANTED: Your original 65816

[David.Empson@bbs.actrix.gen.nz]

In article <1992Dec24.035940.15445@blkbox> jdb8042@blkbox (John D. Baker) writes:
> I know exactly what I'm talking about.  I've seen a 65816-4 (took the cover
> off a IIgs and looked because I was skeptical to begin with) and it was
> most definitely a 40-pin DIP (later models of IIgs may have used one that
> came in a different package and I can't really vouch for what the acclerator
> boards use) and while some pins have been re-assigned, those are
> are not connected in the //e anyway.

All IIgses have 40-pin DIP 65816s.  The ZIP uses a PLCC 65816 (square
pack) which has 44 pins.  The 4 additional pins are power and ground.

The 65816 _might_ work in a IIe, but doing so is a very bad idea.  The
pinout differences are as follows:

Pin  65802/65C02/6502      65816
 1   Ground (input)        Vector Pull (output)
 3   Phase 1 out           Abort (input)
 5   No Connection         Memory Lock (output)
 7   SYNC (output)         Valid Program Address (output)
35   No Connection         Emulation mode (output)
36   No Connection         Bus Enable (input)
38   Set Overflow (input)  M/X indication (output)
39   Phase 2 out           Valid Data Address (output)

Apart from these pins, the 65816 outputs the bank address on the data
bus during the first half of the CPU cycle.

First note that pin 1 is a ground line on the 6502 and an output 
on the 65816.  It is not good for the chip to connect one of its
outputs to a ground.  At the very least, it will increase the power
consumption of the CPU.  At worst, it could eventually damage the chip.

Next note that the Abort and Bus Enable pins will float, since they
are not connected to anything in a IIe.
Having floating values on these pins will cause random behaviour.

It appears that the IIe doesn't use the 6502 clock outputs.

The bank address output by the 65816 would interfere with video
accesses to the RAM.


All in all, it is a bad idea to try to use a 65816 in place of a 6502.
Get a 65802 instead.  They were designed as a pin-for-pin replacement,
and they are reasonably cheap.

A 65802 will not allow you to address more memory.  All it gives you
is the ability to use 16-bit CPU registers when running in 'native'
mode.  A 65802 will not run any faster than a standard 6502.  You
should be able to put a 65802 into a TransWarp IIe, but there is no
'65802 ZIP Chip'.

There are very few programs that take advantage of a 65802 in a IIe.
The only one that comes to mind is Merlin 16 (the assembler) which will
run in a IIe with a 65802, or in a IIgs.  It is a lot faster and more
powerful than Merlin 8.  Note: I'm NOT talking about Merlin 16+, which
requires a IIgs and GS/OS.  All three assemblers come in the same package.

You can, of course, write your own programs to take advantage of a 65802.
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand