Re: 65816 abort line on the AppleIIgs

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

Matthew Montchalin <mmontcha@OregonVOS.net> wrote:

> Pin 35 on the 65816 is for inputting aborts.
> 
> How was this line originally handled when the AppleIIgs was first
> marketed?

I don't recall it ever being used for anything significant and
widespread.  It might have been used in some obscure hardwrae for
assisting with software debugging, in special hardware for testing the
computer at manufacturing time, etc.

It can potentially be used to implement a virtual memory system, but the
IIgs architecture might not be able to support this.  I'd have to dig
out the firmware and hardware references to see if they have any
relevant comments.

I don't think it is used internally by either of the IIgs accelerators
(ZipGS and TransWarp GS) - they just tweak the clock to the CPU as
necessary.

-- 
David Empson
dempson@actrix.gen.nz