On Feb 25, 1:30=A0am, demp...{at}actrix.gen.nz (David Empson) wrote:

> It appears that the monitor always forces fast mode while it is active
> ($C036 contains $80), no matter what the Control Panel says.

I think I remember 'L'isting in Monitor at (visually) slow and fast
speed after changes through Control Panel. Could it be that only key
waiting is switching to fast mode?

> The monitor saves the speed register on entry (e.g. CALL -151 or when a
> program executed with G returns) and restores it on exit (e.g. when you
> use a G command or Ctrl-C).
>
> It also saves the speed register and temporarily forces fast mode while
> waiting for input, so if you use the Control Panel to change the speed
> while at a prompt in BASIC, it doesn't stick immediately.

Any faintest idea why speeding while waiting for keypress? It's beyond
me, totally.

BTW, excellent analysis.


> > Problem with scanned copies is that one cannot search. :-)
> Same problem with my physical copy, so I don't see how you are any worse
> off. :-)

Haha, you're right (but I'd prefer the hardcopy anytime).

> Mega II isn't involved in DMA to fast banks (it has no knowledge of
> memory outside its own two banks).

Mega II is connected to the expansion slots. Even if DMA is done to
fast banks, it's still at 1 MHz.
There should be handshake between Mega II and FPI, but I need some
time to investigate.

> The FPI is in charge of all memory accesses (both CPU and DMA), and only
> hands them over to the Mega II when addressing banks $E0 and $E1
> (possibly via shadowing). If the IIgs is runing in fast mode, it
> requires a sychronization between the 2.8 MHz cycle an the 1 MHz cycle.
>
> For a DMA cycle to fast memory, the FPI gets the bank from its DMA bank
> register, and handles the entire thing without touching the Mega II.

Umm, I think the Mega II signals to FPI (and then reaches CPU possibly
by means of RDY) that there is a DMA and FPI allows or disallows
depending on the bank register.
But I'm shooting in the dark.

> > > > Speaking of which, does anyone have schematics of ROM 03?
> > > They are in the 2nd edition of the IIgs Hardware Reference.
> > My scanned copy doesn't have the Addendum.
> There is no addendum, just fold out sheets at the back of the manual
> with two sets of schematics (256 KB and 1 MB logic boards).

I have only 2nd edition PDF from a cool French site which doesn't have
Addendum/foldout included in the scan. Maybe because the scan is at a
low resolution (for small PDF files) and schematics would be beyond
recognition. In any case, big thanks to the people who did the scans
and put it online.

Anybody in possesion of scanned ROM 03 schematics feeling like wanting
to share?
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