[Coco] [Color Computer] Multi-Pak Question

[Robert Gault]

seanrussoct08 wrote:
> Hi all coco-ers!
> 
> I have a quick question.  I have a multi-pak 26-3124 that i bought off
> of Ebay a few years ago and haven't used it much.  
> 
> I had a friend several years ago tell me that he thought you could use
> one of these multi-paks to access more than one device at a time, but
> i didn't think you could.  Could someone settle this for me? and if
> yes, how do you?
> 
> 2nd, if i buy the hardware from cloud9 to convert this to a coco3
> capable multi-pak, will it never work on my coco2 again?
> 
> Thanks,
> 

Upgrading the multi-pak for Coco3 use will in no way cause a problem 
with Coco1 or Coco2 use. These upgrades are completely safe regards 
backwards compatibility.

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.