[Coco] De0-Nano 6809

[Bill Nobel]

Hey all,

Just got my DE0-Nano  doing Grant’s project with a 512k SRAM (only using 64k).  I noticed right away that Grants basic has a bug in the ?MEM routine as it returns a signed integer instead of unsigned.  Also I have not been able to go beyond 10Mhz, as I am using a AS6C4008 @ 55ns SRAM. The other thing that is confusing me is, if I connect VCC on pin 32 for the SRAM I get no operation.  If I leave it at NC it works perfectly, whats up with that?

I was having trouble getting the external RAM working, so I was roaming the web and really decided to look very closely at Roger Taylor’s pics and a few others and noticed they had the SRAM on GPIO1 vs what I had on GPIO0.  Changed it up and I have better video and full 64k.

Now I need to merge in Neil Crook’s MMU and a few things picked up from the N8VEM group (they have greatly expanded the FPGA options).

This will give a full 6809 Level 2 Nitros9 by the time I am done the port and additions.  It won’t be Coco3 compatible, but it will run non-graphic/windowed (or straight terminal) programs from CC3 under OS-9.

Bill Nobel