[Coco] DW4 Nitros9 and floppy disk access

[Arthur Flexser]

What was going on is that when you booted up with HDBDOS selected, the ROM
was copied to RAM because you're using a CoCo 3, where the ROMs are
normally run out of RAM.  So then, you could manually switch the MPI to
Slot 4 to allow floppy operation without crashing or unselecting HDBDOS
because by that time HDBDOS was running from RAM, so its being active
wasn't affected by the MPI selector switch.

Art

On Sun, Jan 13, 2019 at 3:13 PM Arthur Flexser <flexser at fiu.edu> wrote:

> Walter, now that I read your description of the drive's behavior with the
> various slot selected, I think I understand the problem.  You want the
> HDBDOS ROM to be selected (slot 3), but the floppy drive hardware (slot 4)
> to also be active.  This is a situation where you want the two nybbles of
> $FF7F to be set differently, with one digit selecting slot 3 and the other
> slot 4.  So the value you want to poke into $FF7F is either $23 or $32--I
> forget which nybble is which.
>
> Art
>
> On Sun, Jan 13, 2019 at 2:53 PM Arthur Flexser <flexser at fiu.edu> wrote:
>
>> The MPI slot setting can indeed be changed with software.  Location $FF7F
>> controls this.  The values are $00, $11, $22, and $33 to set the slot to 1
>> to 4.  You also can set the two nybbles separately, though my memory is a
>> bit hazy on what each does.  One hex digit (set to 0-3) selects which slot
>> contains the ROM that is looked at.  The other selects what the SCS line
>> controls, I think, so that if you are doing pokes that affect the hardware
>> of a cartridge in one of the slots, like an RS232 Pak, that slot could be a
>> different one than the one that the ROM is being read from if you set $FF7F
>> correctly.
>>
>> Art
>>
>> On Sun, Jan 13, 2019 at 9:13 AM Walter <zambotti at iinet.net.au> wrote:
>>
>>>
>>> However I'm not sure I like changing the MPI selector while it is on!
>>>
>>> Is there a way I can do this via software?
>>>
>>>
>>>