[Coco] FPGA CoCo and video

[jdaggett at gate.net]

Frank

Correct that there are several camps as to what an "upgraded CoCo" might be. If one wants 
to stay with off the shelp development boards then the Digilent Inc Spartan 3 Starter Board 
with the XC3S1000 part is $159. Its limitations are the board has to be modified just to get 6 
bit color if it can. Also it has only 1Meg of SRAM on board. The Nexys2 board with the 
XC3S500E is $129 and $169 with the XC3S1200E part. This board has PSDRAM but it is 
16Mbyte and has 8 bit color. For $225 there is the Spartan3E-1600 development board. Then 
there is the Altera DE-1 board that can be had for around 4160 to $200 depending on vendor. 
You may even find used ones on EBAY. 

For me I have toyed with the idea of a doing a layout similar infeatures to the Nexys2 board. I 
would use true SRAM or SDRAM instead of the Cellular PSDRAM on the Nexys board. i 
would consider even dropping the FX2 high speed connector for a more conventional 
connecetor. Also the FPGA would be a XC3S500E in a 208 PQFP to keep the board to a 
max of 4 layers. Board size would be no more than 5.25" x 4". Orders in the range of four at a 
time would be about $50 each for the bare board. Populated would push upwards to the $200 
range. 

Adding floppy disk conroll is not an issue. I have a WD1772 core that will also access 3.5 in 
HD floppies. A psuedo MPI board is also rather easy. 

just some thoughts 

james
  

On 18 May 2010 at 16:54, Frank Swygert wrote:

> I find it interesting, but as Mark noted, there are several camps as to what an "upgraded CoCo" should be. I personally don't think a cartidge port is important, but some form of I/O for experimenting purposes is, and the I/O port, at least as a pin header if not a cartridge slot, is probably the easiest way to go. The ability to connect a 5.25" 360K floppy might be a good idea, though even that can be worked around. Most CoCo works are available as .DSK files or some other format over the Internet now, so is it REALLY important to have a floppy drive? Desireable, yes, but could it be lived without? Also I think yes. Using a standard PC keyboard is again a big convenience. Someone mentioned that they would like the ability to use a CoCo keyboard, but at what cost? Basically something like the Puppo adapter would be needed on the circuit borad, only in reverse. Well, maybe use a genuine PIA and that circuitry, but then you need ROM code and such too. A PC KB is much easier a
 nd
>   cheaper. So there are lots of considerations. 
> 
> The board used for the display is a general purpose experimenter board for the Altera FPGA used. I custom board might be cheaper, but only in quantity. Are there even 50 people willing to spend around $200 on a small board CoCo? Especially with the inevitable compromises that would have to be made -- PC KB, maybe a double row pin header instead of a cart slot (of course someone could make an adapter for that), maybe no floppy drives, etc. Some or all of those may have to be done to keep cost and complexity down, and it will still run in the neighborhood of $200 whether an existing experimenter board is used or a custom PC board is made.  
>