[Coco] CoCo3 MMU Register question...

[Joe Grubbs]

I think the General Instrument chip in the Speech & Sound pak is a good 'un, but give full access to all of its registers so programmers can go nuts with it. 



> From: zippster278 at gmail.com
> Date: Mon, 30 Mar 2015 14:53:46 -0500
> To: coco at maltedmedia.com
> Subject: Re: [Coco] CoCo3 MMU Register question...
> 
> I have an overview of all the connections pretty well mapped out, I don’t think it’d be too hard to implement (as outlined below),
> but if the extra memory isn’t used for anything, well…   :)
> 
> Maybe a sound interface would see more use, and be a better project.  Trying to settle on a project to do after the MC6847 VGA
> board.  Have to keep more than one project going with all the wait times for PCBs.
> 
> I guess I’ll read up a bit on sound chips.  What would be the best one for use with CoCo programming?
> 
> - Ed
> 
> 
> > On Mar 30, 2015, at 2:33 PM, Hugo Dufort <hugo at seshat.ca> wrote:
> > 
> > This looks like an interesting and ambitious project!
> > 
> > The book "Assembly language programming for the Coco3" (1987) by Laurence Tepolt contains many reference diagrams that could help you figure out how the MMU works and how it is connected to the other components. You can find PDF copies of this book floating around the Web. A word of advice though: some informations in this book are imprecise or incomplete. You should complement the information in this book with other reference documents such as "Color Computer 1/2/3 Hardware Programming" by Chris Lomont.
> > 
> > If I had a better understanding of hardware and enough time to start a new project, I'd try to create a music/sound coprocessor for the Coco2 & Coco3 using stock chips from the 8-bit era (e.g. the MOS 8580). There ought to be a way of wiring a sound chip directly to the board and communicate with it using a small range of memory addresses.
> > 
> > Hugo
> > 
> > Le 2015-03-30 14:53, Zippster a écrit :
> >> I have a scheme in mind, using a CPLD for address decoding, and high speed latches
> >> for the MMU bank registers, that would operate similarly to one set of CoCo3 MMU banks.
> >> 
> >> With 8 banks (0-7), the same register locations in memory as the first instance in the CoCo3 (TR 0).
> >> Using each memory location ($FFA0 - $FFA7) to hold an 8-bit value for the memory block to map to (in a latch).
> >> 
> >> Perhaps someone who knows about OS9 can tell me if a simplified MMU scheme like this would be
> >> suitable to compile OS9 to use.  This is without a second task register, and no ability to read the MMU registers.
> >> Those things could be implemented if necessary, but trying to keep it simple.
> >> 
> >> Any thoughts or suggestions?  Unfortunately I don’t know squat about OS9’s memory usage.
> >> 
> >> - Ed
> 
> 
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