[Coco] Re: Coco Repack

[jdaggett at gate.net]

Mark 

The MMU is real simple. It is basically a 2 to 1 4 bit wide multiplexor that feeds a 
16x8 ram. The GIME chip uses a 16x6 ram. Most  likely the package was limited to 
68 pins by Tandy and cost factors. Next standard size up is 84 pins in a PLCC 
package. Given that during the 80's it was around 10 cents a pin for package cost, 
another 16 pins would have meant another $1.60 for the part. 

I really believe that many of the limitations of the GIME chip is solely due to keeping 
costs to a bare minimum. 

The VGA portion is tough to code and will occ py the most territory. That will 
determine how big the FPGA is and how much any project like th is will eventually 
cost. Most of the free VGA cores are more modern and do not cover CGA 
resolutions. Or they are very generic and need more work to make them compatible 
to 8 bit buss. One of the nice things is that the software to design the logic and 
program the FPGA is free. Right now I am designing the logic for the two registers 
at $FF92/3. These registers do a dual purpose. They enable interrputs and also act 
as interrupt flags. When you read the register, the flags are cleared while the 
interrupt remains enabled. Not a simple D-FlipFlop latch. Most of the rest of the 
registers are just that, D flipflop latches. 

Then there will be the 2 to 1 (21) bit wide multiplexor to switch between video 
memory and program/data memory. The hardest part is keeping remebering that 
the 6809 latches data out of the CPU on the falling edge of the Qclk and latches 
data in to the CPU on the falling edge of the Eclk. Have to keep in mind when the 
data needs to  be presented to the CPU and when the CPU is passign data to 
external devices. After all that the first half of the Eclk cycle is doing display. 

Mark, like I stated in the beginning, I got started with this to use the Coco as a 
postion controller and database for my telescopes. One thing that I wanted was to 
be able to drive an LCD panel of some type and have OS9 boot from a flash card or 
flash memory. I wanted at least 2 megs of sram and not dram. IDE interface and at 
least 4 mbytes of flash for storage.  

Real pipe dreams was to add firewire or USB and a parallel port to control a CCD 
camera for astronomy.

So this will start as a home project and I have no idea of where it will go. I  have 
toyed with the thought of a FPGA version of the 6309 and run it at say around 15 to 
25 MHz. These are future t hings to work on. I am right now having fun with it and 
learning VHDl in the same time frame. It is amazing what you can do with CPLDs 
and FPGAs. Some of the software development boards that I designed years ago 
would be more flexable and easier had I done a lot of the simple glue logic in these 
devices. 

james  

 
On 6 Aug 2004 at 18:27, Mark Marlette wrote:

Date sent:      	Fri, 06 Aug 2004 18:27:21 -0500
To:             	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>
From:           	Mark Marlette <mmarlett at isd.net>
Subject:        	Re: [Coco] Re: Coco Repack
Send reply to:  	CoCoList for Color Computer Enthusiasts 
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> At 10:45 PM 8/6/2004 +0000, you wrote:
> 
> The 63B09 = 2MHZ, 63C09=3MHZ and 63D09=4MHZ.
> 
> James has quite a project just to do the GIME in a FPGA. Lets not
> overwhelm the project and make it not happen. The paragraph below is a
> HUGE task! Remember this is a hobby for most. To do the software,
> hardware and test takes quite some time. Better yet how many people
> would step forward and help out on it? How about put up the $$$ to buy
> one????? I have over $5k out on the SuperBoard project, that doesn't
> include my time. Love of the machine or stupidity...... :)
> 
> It is quite a simple task to make the memory map for the GIME, it is
> ALOT harder to perform all of the functions that is behind each bit.
> The MMU is simple as well. Interrupt and timer functions are a bit
> more complex and not documented the best. The video with all the
> compatibility modes is something else as well. No doubt something to
> be proud of, the GIME is the machine. I have been in direct contact
> with the creators of this beast and it is AMAZING to me that nobody
> has an internal document of it. I also do believe if they had it, I
> would have it as our conversations went.
> 
> Mark
> Cloud-9
> 
> 
> >IIIRC the 6309 is a 4 MHz part? I doubt it will run reliably after
> >6-8 MHz. Even then, it could vary between chips. If you put a 6309 in
> >FPGA you could drop some of the 6809 compatibility and possibly put
> >in some new code, but then you'd lose program compatibility. Not sure
> >how much that would affect NitrOS9 for the 6309 though. Still, if you
> >do a CoCo repack with the joystick ports and replace the bit banger
> >with USB (or two...), it would be a nice system. Wouldn't be 100%
> >CoCo compatible once the ROMs were in place, but would be close.
> >Would be very nice if the DECB ROM could be modified to use a USB
> >floppy, and maybe HD. But DECB really doesn't need a HD for
> >experimental purposes. Some sort of mass storage would be needed,
> >maybe one of those USB "drives" would be easier to code in the ROM,
> >but you'd have to transfer code from a PC to run DECB programs. The
> >only reason I harp on DECB is the ease of programming for
> >experiments. Basic09 is more powerful, it has similarities t
> >  o Pascal, but CoCo BASIC is so darned easy to learn that for simple
> >  
> > and/or quick experiments it would be preferred.
> >
> >
> >--
> >Frank Swygert
> >Publisher, "American Independent
> >Magazine" (AIM)
> >*Elite* publication for those
> >interested in all
> >aspects of AMC
> >history,performance,restoration,etc
> >.
> >(AMC,Rambler,Nash,Hudson,Jeep,etc.)
> >http:farna.home.att.net/AIM.html
> >(free download available!)
> >
> >
> >
> >-------------- Original message from coco-request at maltedmedia.com:
> >--------------
> >
> > > Message: 3
> > > Date: Fri, 06 Aug 2004 11:30:48 -0400
> > > From: jdaggett at gate.net
> > > Subject: Re: [Coco] Re: Coco Repack
> > > To: CoCoList for Color Computer Enthusiasts
> > > Message-ID: <41136BE8.14904.E66F7 at localhost>
> > > Content-Type: text/plain; charset=US-ASCII
> > >
> > > Frank
> > >
> > > You are ringt if a FPGA version of the 6x09 were incorporated
> > > along with an FPGA version of the GIME chip, breaking the 10 MHz
> > > barrier will be no problem. Speed control can be done with
> > > external clock ship. One by ICT can derive 1000's of frequencies
> > > from a single crystal frequency. In fact the one chip that I was
> > > looking at, from a 28.6868 MHz cyrstal I can derive over a 1000
> > > different E and Q Clocks for the CPU from 400 KHz to 19 MHz.
> > >
> > > My initial intent was to use a 6309 and my new GIME chip and j ust
> > > see how fast I can over clock the 6309. I have two bytes resevered
> > > in the memory map to address the clock PLL chip.
> > >
> > > Just keep pushing the clock until the chip stops.
> > >
> > > james
> >
> >--
> >Coco mailing list
> >Coco at maltedmedia.com
> >http://five.pairlist.net/mailman/listinfo/coco
> 
> 
> 
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