[Coco] Today, I have seen the CoCo 4...

[Mark McDougall]

jdaggett at gate.net wrote:

> If you are referring to the 30 pin SIMM modules using EDO or Fast page
> DRAM, they would be to slow for a soft 6809 in an FPGA. At 25MHz clock
> speed you need 40nS access time or faster. That leaves the newer SDRAM
> chips or fast SRAM to give a soft COCO fast enough memory.

The DE1 has 8MB of SDRAM. There is a relatively simple SDRAM controller on 
opencores that is used on the DE1 in the Zet project. The main issue with 
SDRAM is the latency when setting up a new burst access. In this case you 
can hold off the 6809 if required, but then you run into problems when using 
SDRAM for video memory. Without deep caching, it can't be done.

Regards,

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