[Coco] Coco drives single and double side question.

[Robert Gault]

Ghislain Harvey wrote:
> Well not exactly. What I want is that DIR0 give me the same result as DIR2.
> 

You can do that but only by corrupting your disk operating system and 
reducing the possible number of drives from 4 to 2; not advisable.

The drive table is contained in the DOS ROM and contains 4 values to be 
sent to the controller. The normal values are:
drive #   value
0         1
1         2
2         4
3         $40

In a double sided system where the back side of a drive is considered a 
second side, the values are:
drive #   value
0         1
1         2
2         $41
3         $42

Notice that $40 actually tells the controller to use head #2, back side 
of the drive. Tandy configured the controller so that the side select 
$40 accessed another drive.

The tables are located in the ROM at DOS1.0 $D7AA and DOS1.1 $D89D.

If you want DIR0 and DIR2 to look at the same disk content, change the 
drive #2 value to 1. You had better have a good reason for doing this 
because it is just plain wrong!