[Coco] 6809 FPGA

[Neal Crook]

Hi,
my first post here but I thought I'd throw in a few debug comments based on
my multicomp build

1/ I would also advise configuring some internal RAM, for three reasons.
First, it decouples you from wiring problems. Second, it decouples you from
timing problems. Third, it makes your FPGA self-sufficient to the extent
that you can run logic simulations in Quartus without the need for any
additional testbench stuff. On my build, it took me more than a week to
find that I had an address line short.. not on my breadboard (which I had
buzzed out) but on the daughtercard PCB holding the FPGA (which I had
assumed was good and so had not buzzed out).

2/ The flashing cursor (and implicitly a "raster scan" or the non-CRT
equivalent!) on the VGA is a strong indicator that lots of stuff is working.

3/ Be warned that not all PS/2 keyboards will run on 3V3. Grant's design
has a 3V3 supply and that did not work for me. I had to connect it to a 5V
rail. You can and should still connect the pullups to 3V3.

4/ With the kbd connected you should be able to tap the caps-lock and
num-lock keys and see the kbd LEDs toggle. This is handled entirely in
hardware. The keypress is a message from the kbd to the FPGA and the LED
toggle is a message from the FPGA to the kbd, so if you can toggle the LEDs
it shows another hunk of your FPGA and physical interconnect is OK.

Once you're all up and running, I assume you have a project beyond running
Microsoft BASIC? You might like to check out my multicomp6809 github
repository. The WIKI there describes hardware mods (coco-compatible memory
mapper, timer interrupt, improved clock control) and software stuff (a
debug monitor, a FORTH compiler with SD-card drivers, a FLEX port).

My current work-in-progress is a (level1) nitros09 port, but that's a
subject for a separate post.

Neal.