[Coco] [Color Computer] Multi-Pak Question

[Steven Hirsch]

On Fri, 30 Jan 2009, Robert Gault wrote:

> My guess is that when you bought the unit you did not receive the user's 
> manual. Because if you had read the manual, you would see that not only can 
> you select the active slot by using the switch on the unit but also by 
> POKEing a value to 65407 aka &HFF7F.
> The manual states to use the following values:
> Selected slot      Value
>  1                $00
>  2                $11
>  3                $22
>  4                $33

> A more detailed explanation that supplied by the manual follows. The slots 
> are actually numbered with base-0 notation; 0-3. The nominal value used is 
> the slot value for both the msn and lsn nibbled of the byte, thus $00, $11, 
> $22, $33.

> Actually there are two functions being controlled by the value. The msn 
> selects ROM available to the Coco at $C000-$DFFF, while the lsn selects the 
> I/O device responding to $FF40-$FF5F.

> It is not necessary to use the same value for both msn and lsn. So if you had 
> a device (ex. RealTimeClock) in slot 1 and your disk controller in slot 4, 
> you could POKE &HFF7F,&H30 and retain the Disk ROM in slot 4 while doing I/O 
> through slot 1.

> This also means you could read a ROM in an auto-starting pak without starting 
> the pak. Select the slot of the ROM pak using the msn while keeping the lsn 
> at the default 3.
>
> Doing the above is a bit more complex. You would want to use a short ml 
> program and be sure to clear the CART interrupt before returning to Basic.

Thanks, Robert, for the all-time most coherent explanation of the MP 
programming model!  I have read a number of others (won't point fingers) 
that dance a complete circle around the specifics and leave me scratching 
my head.

This one is getting saved, printed and stuck in the reference binder :-).

Steve


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