[Coco] TC-9

[jdaggett at gate.net]

On 7 Jul 2008 at 19:39, Chuck Youse wrote:

> On Mon, 2008-07-07 at 18:02 -0500, Mark Marlette wrote:
> > Chuck,
> > 
> > There are free CPU cores, etc. Some have dabbled here but there is
> > no  GIME FPGA, others will say it isn't that hard, etc. Proof is in
> > the  pudding. If it isn't that hard, then do it, no time, busy,
> > etc...Not  implying you here.....There is a lot going on in the
> > GIME.
> > 
> 
> Well, one of the problems with implementing the GIME as a stand-alone
> FPGA stems from the fact that the GIME performs quite a few analog
> functions, and the digital functions on any suitable FPGA will be at
> the wrong voltage levels.  E.g., composite and RGB outputs, not to
> mention the clock generation - as I'm sure you know the 6809 likes to
> drive its internal circuitry off the E clock.  So any drop-in GIME
> replacement would have to be a board of sorts, an FPGA with some
> external components.  
> 

The only analog functions are the composite video from the internal DAC the RGB DAC 
and the oscillator circuitry on board. The oscillator and its quadrature phase is rather easy 
to do in an FPGA given the modern DLL/DCM in most chips. 

> If it's a matter of implementing a 6809 + GIME on a chip and
> interfacing that to an external bus, that's one thing.  If it's a
> drop-in board to replace the GIME, that's another.  But as I stated
> before, if you're going to go that far, might as well integrate a lot
> more into the FPGA.
> 

For my needs, whether the CPU is integrated or not is only a nicety.

> If your comments were meant as a gentlemanly challenge, I'll take it!
> But I want a free AT keyboard interface for my CoCo when I finish ;)
>

No, just made a suggestion. SInce you were talking about essentially recreating a COCO3 
in discrete logic. I learned long ago that never fall inlove with your designs. Someone will 
always have a betterr or cheaper way. Learned that early in my engineering career. 

> A suitable FPGA with more than enough area for a 6809 and GIME (with
> room to spare) would be an XC3S250E - the 144TQFP/4ns speed grade runs
> ~ $15 at qty 1. 

I have an XC2S300E in an FT256 BGA package on a board now. And yes the GIME and 
the 6809 will fit with plenty of room and more I/O than I need. 

> > I tip my hat to you and your FDC controller project!!!! Nice job.
> 
I am not really doing a FDC controller. I just came across a core one day about 4 months 
ago and found it interesting. It just proved to me that a FDC could be done in an FPGA. I 
have the core and may one day do something with it.

My requirements right now is a small, portable and battery operated embedded board. The 
key requirement is small and with either a minimum of 512K of sram and and SPI flash or 
8K of sram and 2MB of parallel flash. Currently leaning towards the large SRAM and serial 
flash. A 6809 processor would be nice since I am familiar with it. An HC11/12 would also 
suffice. Actually leaning to do something like embedding HC11 periherals around a 6809 
core that is freely avaialble. Kind of like a HC11F1 with a 6809 core instead. 

james