Re: Microsoft Softcard and IIgs

[vladitx <vladitx@nucleusys.com>]

On Mar 12, 9:10 am, Alex Freed <alex_n...@mirrow.com> wrote:

> I'm not sure the issue is so subtle. What happens is that since the
> SoftCard and clones use Apple's main memory, they can only do so
> during the 500ns when the 6502 normally does it but not the "video"
> 500ns.

Yep, the phi0 portion.

IIgs goes way more complex with the MegaII/FPI bridging.

> Applicard on the other hand has its own memory and only talks to
> the 6502 via a pair of registers. The way the "busy" flags are
> implemented it doesn't matter if z80 runs at 20 MHz and 6502 at 1 MHz as
> is the case with my kind-of-replica card. By the same token the Apple
> can also run at any accelerated speed.

Definitely the PCPI design takes the least-resistance path and
decouples the Apple II and the Z80 system as much as possible, at the
cost of  losing the direct access to Apple II memory.

I'd guess that screen scroll suffers from this. Another guess is that
probably GBASIC doesn't work on Applicard?

> I have a ROM1 GS and a SoftCard clone. If you want I can test it.

01 and 03 should be identical in the slot operations, but yes, if you
find the spare cycles and feel interested - please do.

I will dedicate a day (no plans, though) to plug the analyzer in IIe
and IIgs and see what's wrong. M$ SoftCard is the only DMA card I have
so far.