[Coco] Coco drives single and double side question.

[Mike Pepe]

Ghislain Harvey wrote:
> What I really want is that my system react as if I have 2 single side drive.
> 
> I have 2 double side drive.
> So that's why I say DIR2 will give me the same thing as DIR0
> 

Having drive 2 read the opposite side of drive 0 is a hack.

The question is, how is the hack done?

You can accomplish this with a chip or two and some rewiring in your 
disk controller, or by patching the DECB ROM to drive the correct drive 
select lines. (the ROM patch is probably more common)

The signal line the CoCo uses to select Drive 3 is actually the line 
that is used more commonly to select sides on a double sided drive.

So, what should happen in a normal two drive system is that DIR0 reads 
drive 1. DIR1 reads drive 2. DIR2 and DIR3 would IO ERROR out.

If DIR1 reads the first side of the second drive, congratulations, your 
system behaves just like a normal single sided 2 drive system. Nothing 
else needs to be done.