[Coco] De0-Nano 6809

[Dave Philipsen]

Yes, Grant's BASIC is just a stripped down version of Microsoft's Color BASIC for the CoCo. I don't think It has ever had the ability to show more than 32K of available memory for BASIC programs with  ?MEM.  Technically, you can open up extra RAM that would have been occupied by the Extended BASIC firmware and it should work but since the CoCos were never really designed to do this you are moving into unchartered territory perhaps.

As far as the SRAM goes that's pretty weird. I think you need to go over your wiring with a fine-toothed comb. I cannot see how the SRAM would even function without VCC connected. The DE0 uses 3.3v on all of the I/O right? And you're using 3.3v for the VCC right?  I know pin 32 is connected to VCC (which is 3.3v) on both of my projects.

I don't know what the difference is between GPIO0 & 1 on the DE0 but it is suggested that you keep all the address and data lines of a memory device on the same internal FPGA bank or at least spread across two adjacent banks.  That is a recommendation by Altera. Probably a good idea for your video lines as well since they run at pretty high speed (25 MHz).


Dave Philipsen

> On Oct 29, 2015, at 12:31 AM, Bill Nobel <b_nobel at hotmail.com> wrote:
> 
> 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
> 
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