[Coco] [Color Computer] Floppy contoler Q

[Robert Gault]

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.