Re: Twilight zone?

[mjmahon@aol.com (Michael J. Mahon)]

Willi Kusche wrote:

>"Bill Garber" <willy46pa@comcast DOT net> wrote in message
>news:<ct-dnZo4hITLNCndRVn-jw@comcast.com>...
>> This is not a reason, or the why, but mine does the same
>> thing once the drive is fully partitioned and formatted.
>> Maybe it is finding your present drive, but looking for
>> an additional drive. Are they capable of Master and Slave
>> adaptation?
>
> I figured out why PARTITION.MANAGER sometimes can't find a Vulcan card. 
>It looks at $CxFB and if bit 0 is set then it decides that there's no Vulcan
>card in that slot.  I looked at $CxFB before booting the IIe and it was $00. 
>So, PM can find it.  But after booting and accessing the Vulcan drive, $CxFB
>is now $FF.  A bit disconcerting to find variable data in a ROM area.

Question:  When does a ROM address not have a constant value?
Answer:  When it is bank-switched.

The Vulcan ROM (and SRAM) are heavily bank-switched, and there
is no rule about keeping the $Csxx space un-switched.

If you disassemble some of the ROM code, starting with the Reset
state, you will see how the bank selection works and can then explore
the entire ROM without dumping it.

(I did this about twenty years ago, and don't have my notes handy.  ;-)

-michael

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