[Coco] [color computer] Just imagining...

[Phill Harvey-Smith]

jdaggett at gate.net wrote:
> Phil

James, sorry to be anal about this but the correct spelling of my name
is >>> Phill <<< :)

> Small more modern FPGAs are now approaching the $10 range.  Some of
> the older small FPGAs are still a bit pricy. In comparison single
> unit price of a Spartan 2 15K gate versus a Spartan 3 50K gate is
> virtually even. $10.89 for the older part and $10.10 for the newer
> part. More capacity and not much difference in cost.

Yeah I have often wondered if I should have a play with FPGAs, I have
used some CPLDs, notably the Xilinx XC95xx and XC95xxXL series.

> CPLDs are even still cheaper. The major problem in usig FPGAs and
> CPLDs is most are designed for 3 volt logic levels.  There are still
 > some that have 5 volt tolerent inputs. You can do a lot in some of

I have used the 5v & 3.3v tollerent ones, and they do work well and 
interface with 6809 stuff quite easily :)

The other pain for the home constructor is they are mostly surface 
mount, which is doable but much harder than either PLCC or DIP which can 
be socketed :)

> the CPLDs and small FPGAs like MMUs. UARTS, IDE interface, SPI, PS2
> interface, and even a simple video unit. One approach is to use the
> current 6x09 and three or four CPLDs or a couple of small FPGAs. Or
> use one big FPGA.

Yeah I'd always thought about using some of the classic major chips,
6x09, 6821, 6845 etc, that way we can be 100% sure of compatibility :)

> The idea of going to a Spartan 3 is this device ranges from $25 for a
> 200K gate equivalent to about $55 for a 1 million gate equivalent. A
> XC3S1000 (1 million gate equivalent) can house the complete Coco3
> with room to spare. You might even be able to squeeze the whole Coco
> 3 into XC3S400 (400K gate).  With a 1.5 million gate Spartan 3, one
> can put the whole Coco 3 in one plus a Math Coprocessor. Everything
> could run at about 25 MHz also to boot.

That would be cool, though don't the versions of Webpack to program the 
denser gatecount chips cost real money ? Though I guess you can 
illiminate this by using a couple of the smaller chips. Though in some 
ways that makes the design more complex.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.