6502 Playground

[GARTHWILSON]

Quote:

I would have to either zig-zag the line and am not sure what it will do to signal reflections, with all the 90-degree turns,

If it's against a true ground plane (pours don't qualify), the answer is that the bends don't hurt anything. See Dr. Howard Johnson's article, "Who's afraid of the big, bad bend?". There is no need to keep traces at 0, 45, and 90 degrees though. It may look neat, but it doesn't help signal integrity or circuit density. If going to odd angles allows you to straighten it out and get it shorter, go for it.

[enso]

PCB manufacturers

Good to know. I use oshpark.com - they aggregate PCB designs and do daily runs of 2-layer boards and somewhat less often for 4-layer boards.
2 layers: $5.00 per square inch, 3 boards (if your design is 1"x1" you get 3 boards for $5.00).
4 layers: $10.00 per square inch/3
free shipping
currently gold-plating boards although no promises
same disclaimers apply

[enso]

Zigzag traces... Since the FPGA is rotated 45 degrees, a horizontal 5mil trace cannot clear the pads. The closest you can do is a /\/\/ zigzag around every pin. Looked scary across 10+ pads.

[MichaelM]

If not scary, at least tedious and error prone. I have access to PCAD and I don't like do that kind of routing manually with that tool unless it is necessary to make a patch without moving too many traces, and no components. Your solution of moving the oscillator is probably best anyway.

[Arlet]

enso wrote:

are there any pin limitations for outputting a clock from the DCM out?

All you need is a regular IO pin. Since you only need 14 MHz max, it's easiest to use an internal clock at twice that rate, and just implement a toggle flip flop on the output.

[enso]

Cleaning up the board. There are 15 extra FPGA pins now connected to tiny pads just big enough to solder a wire-wrap-type wire. So it's possible to do Garth Wilson's SRAM stacking.

I will order 3 boards this week. The heating elements for the hotplate are due to arrive as well - I have the PID controller, the SSR and aluminum ready to go.

If anyone cares to review, here is the GEDA PCB file:

http://apple2.x10.mx/6502play.img/6502playground.A.pcb

6502.org wrote:

Image no longer available: http://apple2.x10.mx/6502play.img/6502playgroundA.front.2.png

6502.org wrote:

Image no longer available: http://apple2.x10.mx/6502play.img/6502playground.A.back.2.png

Minor changes include:
-1.2V regulator runs off 3.3V

[Twylo]

This is a really cool project - definitely count me in if it's not too late!

[enso]

Not too late at all. I now have about a dozen XC3S700ANs and even more 128KB SRAMS. After testing (and probably making minor revisions) I should be able to bang out at least 10 units, $60 each for this forum.

I am working on an Apple II mainboard with keyboard, paddles, VGA or composite and CF slot. I hope you guys can make or help me make some other machines...

Send me a message and I will add you to my list.

P.S. I hope I am not violating any board rules. I am not soliciting business (as you can judge by the price that probably does not cover the component costs). 6502 machinery is more of a religion practice for me.

[GARTHWILSON]

enso wrote:

P.S. I hope I am not violating any board rules. I am not soliciting business (as you can judge by the price that probably does not cover the component costs). 6502 machinery is more of a religion practice for me.

Since you're promoting our interest, it's no problem at all. The ones we kick out are the ones who come to sell handbags, watches, insurance, iPods, phones, movies, vacations, etc..

[enso]

Finally the first prototype boards came in. A 100 Forint coin is for reference

[ElEctric_EyE]

Any proress with your BGA project enso?

[enso]

A family member died tragically and unexpectedly. I've been unable to spend any time on this project.

My hotplate seemed to work well, but the initial board failed to configure - as expected. I created a test board with just JTAG and power connections and a couple of leds. Fabrication was delayed with christmas/new year holidays. I haven't had a chance to try the test board. At this point I can hardly remember what I was doing...

I will try to get back to it. In the meantime if anyone wants the schematics/layout in gEDA format, let me know.

[ElEctric_EyE]

I'm very sorry about your family loss.

Thanks for posting an update.

Your prior postings on BGA soldering using your custom hotplate config were most inspirational. I look forward to your future posts.

[whartung]

Condolences enso, no hurry.

[BigEd]

Sorry to hear that enso: my condolences too.