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

[jdaggett at gate.net]

Phil

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.

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 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. 

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. 

Doing an imagining session, one can let their ideas take them anywhere they want. I 
currently have access to a 6809 core that is supposed to run at 12 MHz. I have a Spartan 
2E (300K gate equivalent) development board and the CPU core will take up about 2/3rds 
of it. An improved GIME with expanded video takes ups about 50K gates. Two UARTS and 
a parallel port and IDE should fit in the remaining with maybe some room left over. Alot will 
determine how complex the UARTS will be. 


james 

On 31 Jan 2006 at 20:36, Phill Harvey-Smith wrote:

Date sent:      	Tue, 31 Jan 2006 20:36:20 +0000
From:           	Phill Harvey-Smith <afra at aurigae.demon.co.uk>
To:             	CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Subject:        	Re: [Coco] [color computer] Just imagining...
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> Though I guess the thing that complicated this case was the MMU 
> implemented in LS+a few pals+some static ram. Guess if you where doing 
> it now, you could get away with just the major chips a couple of 
> CPLDs/FPGAs, and do it in less than 20 chips :) (I'm asuming you don't 
> want to bury the whole thing in a big expensive FPGA).
> 
> Phill.