[Coco] Coco drives single and double side question.

George Ramsower georgeramsower at gmail.com
Tue Jan 8 22:45:24 EST 2008

I finally remember how I did the double sided two drive system using RSDOS 
on a coco.... I think.

I may have the polarity wrong on the diodes, but I'm sure this is the basic 
layout. I do remember using germanium diodes to minimize the voltage drop.

This makes D0 side one of drive 0, D1 side two of drive 0, D3 side one of 
drive two and D4 side two of drive two.

 I"m not going to test this, but if someone can see it's wrong, then it's 
okay to throw rotten tomatoes at me. It's been many years.

Here's the link for a small, quickly put together image... the coco 
controller is on the left and the drives are on the right... in case my 
image isn't clear.



----- Original Message ----- 
From: "Mike Pepe" <lamune at doki-doki.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Tuesday, January 08, 2008 8:59 PM
Subject: Re: [Coco] Coco drives single and double side question.

> 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.
> --
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> Coco at maltedmedia.com
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