Re: New CBM-II discoveries

Mia Magnusson wrote:

> (Not that obvious for me :) )

"Obvious" in the sense that the original BIOS is posted on Zimmers for
everyone to see :-)

> Btw I don't know what a PC BIOS does here. Maybe there is some kind of
> "standard" for some identifying strings/data there?

The original PC BIOS did have some magic values to determine the model
(PC vs XT and so on). Other manufacturers used this technique too but
each one used a different location(s) and values. DOS-PLUS looks up
various locations in the BIOS to determine the machine on which it runs.

> My main concern is the (rather small) risk of someone starting the 6509
> software for the 8088 card while having a Z80 card or vice versa.
> Probably not a big problem, but still...

With regards to this, the original software does not even check whether
the card is present - it happily loads itself into $0800 and jumps
there, without even noticing that the RAM chip is not present there.  So
I wouldn't really worry too much about it :-)

> Btw in a theoretic future a recreated CBM-II motherboard could have
> hardware for hooking up more than one coprocessor card. That would need
> some way to select which coprocessor card that should be enabled. In
> that scenario there needs to be some logic to make sure the user
> doesn't run software for another card than the active hardware.

I suppose there should be then some additional I/O chip in bank 15, for
managing the additional features of the mainboard?
Regards,
Michau.