[Coco] TC-9

[jdaggett at gate.net]

On 7 Jul 2008 at 13:14, Chuck Youse wrote:

> On Mon, 2008-07-07 at 10:06 -0500, Joel Ewy wrote:
> > I have a TC-9, Chuck.  I have to say I've never been able to put it
> > to very good use.  It (mine at least) was always a bit flaky in
> > operation. One of the main problems I had with it was that I could
> > never get a hard drive hooked up to it.  For some reason, it was
> > incompatible with the Disto SCII, which I already had.  So no
> > no-halt floppy, and no 4-in-1 for RTC and SCSI.  Before I got that
> > figured out, I bought an MM/1, and the Tomcat sat mostly unused.
> 
> Man, I'm a tad bit jealous - I want! I want!  :)  And btw, building a
> hard-drive interface for the thing would mostly likely be a piece of
> cake.. it doesn't get much easier than an IDE interface.
> 
> Does it have any custom chips on it that you're aware of?  One big
> problem with making a Coco 3 clone is the GIME.  If the TC-9 did most
> of the naughty in PAL/GALs and discrete logic, then I might try to
> resurrect it..  The Coco 3 is a nice machine, but for 'serious' work
> it has some limitations, the poor keyboard, case, RS-DOS/Coco2
> compatibility stuff ...
> 

The GIME chip is not that mysterious in that its functions can very well be done in a 
FPGA. Besiues RSDOS is more than capable for most uses. Granted the Coco2 
backwards compatibility can be a limitation. But not in an FPGA based system with a 
large enough logic cells. 

> My ideal NitrOS-9 machine would have no bells and whistles on-board,
> and just lots of expansion slots.  I'm debating using a 63C09 and
> creating a custom MMU (which would cause problems with NitrOS-9,
> because I'd use a simpler mechanism than the GIME) or putting these
> handfuls 68008s or 68000/68010s to use and making NitrOS/68000.. I'm
> leaning towards the latter, if only because that eliminates the need
> for a DAT, and OS-9 lost a lot of its elegance when the MMU was
> introduced (Level 1 -> 2).
> 

The MMU is rather simple in design. The basic design in the GIME according to the 
service manual uses a single port ram and a mux. In an FPGA this can very well be 
done with an assynchronous dual port ram. 

> But if I had schematics for a TC-9, well then .. I might steal the
> design.. wonder if Mr. Puppo would mind.
> 

You still are limited to 4 MHz max. A 6809 in an FPGA is doable to about 25MHz. 
With a big enough FPGA, like a Xilinx XC3S500E,  you can add the GIME functions 
plus a WD1772+ FDC and at least one serial port, PS2 mouse and Keyboard,  USB 
2.0 and IDE interface. The MMU can be easily done to access 2MB of ram but why 
limit there? 

Even if  you want to use as 68000, that to can be synthesized in a FPGA. 

james