Re: IIc/UniDisk Crash to Monitor

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

In article <mark-081093111052@128.157.9.145> mark@trillian.jsc.nasa.gov (Mark Manning) writes:
> In article <28ro7iINN3da@iraun1.ira.uka.de>, voss@i40s5.ira.uka.de (Stefan
> Voss) wrote:
> > 
> > |> 205A-       M=00  A=18  X=00  Y=07  P=33  S=F5
> >    ^^^^        ^^^^  ^^^^  ^^^^  ^^^^  ^^^^  ^^^^
> >      |          |     |      |     |     |    |
> >  address where  |     |      |     |     |    |
> >  the crash      | Accumulator|   Y-Reg   |  Stack pointer
> >  occurred (BRK) |           X-Reg        |
> >               dunno                  Processor status
> >                                      (zero flag, negative flag, ...)
> 
> I'm not sure either, but I think the "M=00" is what was contained at
> memory address $205A.  (Which is the BRK command.)

Nope.  "M" is a pseudo-register which is a combination of several
softswitches which control bank switching.

In the IIc, the value for "M" is generated by the interrupt handler by
reading several soft-switches.  The enhanced IIe interrupt handler
does a similar operation, but the monitor doesn't display its value on
a break.

The IIgs has a hardware register at $C068 which performs a similar
function (and the monitor displays it as "M").
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand