[Coco] Electronics Newbie question

[John Kent]

Yes ...
I was going to suggest KiCAD too. It's what N8VEM uses for his Z80 / 
S100 / Eurocard boards

You can get a standard edition of Eagle CAD for a couple of hundred 
dollars, but it restricts you to 160mm x 100mm Eurocad size boards. 
there might be a free version of Eagle but it limits you to a fairly 
small board size.

There is also PCB express or express PCB who provide some free schematic 
capture and PCB layout software, which is fairly easy to use and runs on 
windows but you have to get the PCBs made through them.

I wrote a long email explaining the virtues of using programmable logic 
such as FPGAs and CPLDs, but I decided not to post it. If you were going 
to design an add on board for the CoCo, you might consider interfacing 
to an FPGA or CPLD, so that you can reprogram the function of it.

FPGAs require fairly careful by passing and multiple supply rail 
regulators. You can buy bare bones FPGA boards that have  the regulators 
and configuration flash and clock on them.

http://gadgetforge.gadgetfactory.net/gf/project/butterfly_one/ (XC3S250E 
is $49.99 and the XC3S500E $74.99) or 
http://www.seeedstudio.com/depot/gadget-factory-m-29.html (XC3S250E 
board is $49.90 and the XC3S500E $64.90) and there are other suppliers 
in US and UK.

XESS corporation also make a small 40 pin DIP header board with an FPGA 
on it called the XuLA which comes in a 50K gate version and a 200K gate 
version. The advantage of the XuLA board is that it has about 8MW x 16 
bit SDRAM on it. The 200K gate version I think sells for around US$70.

http://xess.com/prods/prod048.php
http://dangerousprototypes.com/2011/02/20/xess-xula-200-fpgauc-board/

I managed to squeeze a 6809 FPGA core, PS/2 keyboard interface, SDRAM 
controller, serial interface and text based VDU on the XuLA 200K gate 
version, so you could use it to implement a co-processor. The Gadget 
Factory boards don't have external RAM, but there is some synchronous 
block RAM in the FPGA chip that you can use for memory. There are AVR8 
core and other CPU core available on opencores.org so you could put 
other processors in it.

If you were to interface it to a CoCo you would need 3.3V to 5V voltage 
level conversion chips on the interface.
You could design a basic carrier board for the FPGA board which had some 
bus switches on it to do the level translation.

There are projects on the Gadget Factory and XESS corp web site as well 
as opencores.org. There are a list of resources on my web page too.

http://members.optusnet.com.au/jekent/FPGA.htm

You could for instance design a logic analyzer in the FPGA and have the 
trace buffer readable by the CoCo. You could also implement timers, 
pulse width modulators, frequency counters, graphics controllers and so 
on.  The Gameduino is an add on FPGA board for the Arduino that can be 
used as a  graphics controller.

http://excamera.com/sphinx/gameduino/

The XuLA board has a PIC with a USB interface, so it might even be 
possible to interface the USB connection to the CoCo.

The FPGA development software can be downloaded from the Xilinx or 
Altera web site. Be warned though, there is a fairly steep learning 
curve learn how to write verlog or VHDL hardware description language to 
program the FPGA. There is the possibility of designing at a schematic 
block level, but that tends to lock you into particular software.

John.

On 18/12/2011 8:45 PM, Andrew wrote:
> Paulo,
>
> This should probably be a separate thread, but anyhow...
>
> Typically, many people recommend Eagle:
>
> http://www.eaglecentral.ca/eagle/
>
> It's only real downside (other than being "non-free" - that is, 
> non-open source, if that matters to you in any way) is the fact that 
> to go beyond a certain basic level (which you may or may not ever 
> need), the license cost climb into the stratosphere very quickly; 
> however, I've been assured by others that if you are using it for 
> commercial purposes, to design and sell PCBs (or kits, or products), 
> that you'll recoup the cost fairly quickly.
>
> If you wanted something more "open source", then there are options 
> like KiCad:
>
> http://kicad.sourceforge.net/wiki/Main_Page
>
> ...and gEDA:
>
> http://electro.easyb.ch/pages/schem.html
>
> Note that gEDA has a very, very steep learning curve (not that Eagle 
> is going to be easy, from what I understand). I don't have any real 
> experience with any of these packages, but I have looked at them all 
> from time to time. They all have their pros and cons, IMHO.
>
> Finally - a "fun" option (not sure what the status of it is; last I 
> played with it, it was still "buggy", but showed a lot of potential):
>
> http://fritzing.org/
>
> Something to keep your eye on, anyhow...
>
> -- Andrew L. Ayers, Glendale, Arizona
>
> -- 
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco
>

-- 
http://www.johnkent.com.au
http://members.optusnet.com.au/jekent