[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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