[Coco] Last video I promise... :)

[Mark McDougall]

On 12/11/2014 6:29 PM, Camillus Blockx wrote:

> Now, in case if it is possible, a faster , larger fpga could add
> maybe a few shortcomings ( Parallelport, rs232, ps2Kb(just to name a
> few)), and that would maybe justify the higher cost for the fpga.

The current design samples the video RGB output and has no bus interface 
to the Coco itself, so features as you've described are not possible 
with the current architecture.

> Now the big question, would it be possible to redesign your project
> to give te needed speed for the better vga port, plus the added ports
> I mentioned, and what FPGA chip/board wouldthat need?

The use of SDRAM in the design (for the frame buffer) is a limiting 
factor in the speed of the design. In general the cheaper FPGA's are 
limited to around 150MHz for all but finely-tuned designs - ultimately 
the speed is dependent not only on the device, but also the logic you're 
trying to implement.

Another limiting factor (speed) is the use of a discrete successive 
comparator design in the FPGA itself for the ADC's.

A lot of these issues would disappear with a TVP7002 (USD$7.63 from 
digikey). However it's not a trivial device to integrate into your 
design (eg. 100 pins). OTOH the jitter and quality would no longer be 
issues, and you could probably get away with a simple line buffer and 
I2C configuration module in a much smaller FPGA.

I have mentioned all this before on this list.

Regards,

-- 
|              Mark McDougall              | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug> |   with less resistance!"