[Coco] FPGA CoCo's

[Dave Philipsen]

My first attempt was unsuccessful.  The CoCo FPGA Yahoo group has the 
files but the documentation really requires that you had been following 
the project pretty closely.  I purchased a DE1 board, loaded up the 
flash memory as the documentation apparently directs you to do, loaded 
the "sof" file and I did get a screen that looked like a CoCo screen and 
even got a partial Extended Basic boot message but the screen was full 
of garbage and I could never figure out why it didn't fully work.

On the other hand, I have built Grant Searle's Multicomp project first 
using a EP2C5T144C8N  board and now a EP4CE10F178C8N board. The first 
can be had for around 16 bucks on eBay and the second for around 34 
bucks.  This project is not a synthesized CoCo but it is a 6809 
computer  that runs REAL fast (like 25 MHz).  Imagine a CPU running 12.5 
times faster than a CoCo in high speed mode!  The project generates a 
VGA display of 80 x 25 characters with 16 colors (text only), uses a 
PS/2 keyboard and you can run Microsoft BASIC.

I am using it as a platform for some 6809 projects that I'm working on 
that are not necessarily CoCo related.  I've added a 512KB SRAM, DS1302 
real-time clock, and 24FC512 serial EEPROM.  I've got the code working 
for reading/writing to the RTC and I've even got an MMU that emulates 
the MMU in the CoCo 3 GIME so that I can bank switch 8K blocks into any 
8K boundary on its memory map.  Just started learning the VHDL so I am 
far from an expert but I am thoroughly impressed with what can be done!  
Right now, everything fits onto a perfboard in an area of about 15 
square inches.  I have to limit the CPU clock to 16 MHz because I'm 
using a 55ns SRAM chip but hoping to get a 10ns chip going soon.  I'm 
also working on getting the same thing working on the Altera/Terasic DE1 
board but am currently having trouble tweaking the VHDL for the 256K x 
16 SRAM chip.  I'm supposing that the timing characteristics are a 
little different than other SRAMs.

Dave Philipsen


On 5/21/2015 4:18 PM, Michael Brant wrote:
> I have been hearing about people using an FPGA to run as a CoCo. Anyone on
> the list doing this?
>