[Coco] [Color Computer] Floppy contoler Q

[Arthur Flexser]

On Sat, 14 Jan 2006, Robert Gault wrote:

> Bit6 $FF40 is used by Tandy for drive select 3. However, the connection 
> of this bit to the ribbon cable results in it also being a side select.
> 
> When single sided drives are used, bit0=drive0, bit1=drive1, 
> bit2=drive2, and bit6=drive3. With double sided drives and without any 
> hardware changes to the controller or ribbon cable, bit0=drive0, 
> bit1=drive1, and bit6= side select.
> 
> You might think that 3 double sided drives could be used because bit6 
> could be combined with any of the three bits 0, 1, or 2 resulting in 0, 
> 1, 2, $40, $41, or $42. Unfortunately, the controller does not permit 
> that because $00 turns off the drives. That leaves you with 1, $41, 2, 
> and $42 or two double sided drives. You can however, have two double 
> sided drives and one single sided drive at the same time with the third 
> drive selected with $40.
> 

I think you goofed here.  While the bits for DS0, DS1, and DS2 are bits 0, 1,
and 2, setting each one results in $FF40 values of 1, 2, and 4, so the
corresponding double sided versions would be $41, $42, and $44.  So, I don't see
any problem with connecting 3 double-sided drives.

Art