Build something which makes sense for you! It's too easy for projects to lose their way, and never happen.
Cheers
Ed

Thanks, and absolutely true. I am painfully aware of the featuritis issues. I am posting this more as a last-minute effort to catch stupid decisions, which happens when you stew in your own juices too long. For example, adding a couple of lines to the CPU and socketing it as suggested by Arlet, is a minimal change, which makes the whole thing more functional.

I am not movable about the overall design goal -'small and simple'- for this project, and am grateful for your feedback.

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Arlet, to answer your post in the POC2 thread (more appropriate here), yes, I envision an add-on board(s) with:
-VGA output/resistor network
-Keyboard/mouse jacks
-SD card reader
-game controller jacks of some kind

Since the FPGA is doing all the work, these would be pretty much trivial adapters.

_________________
In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Hi enso, if you could arrange for the pinout to allow either 128K or 512K SRAM, that would be a bonus. I'd be happy to buy and ship some 512K parts to you. (In the case of DIP parts, the pinouts are sufficiently compatible to allow that: AS6C4008 vs. AS6C1008)

It's a good point that 48 I/Os is enough to fit an external memory board that's 16bits wide. For 32bits, I'd probably need to borrow some of the CPU connections, or the on-board SRAM connections.

Cheers
Ed

This project is largely about recycling my inventory. I have XC3S200ANs, XC3S700ANs and a bunch of K6R1008V1C-JC10, 128K 10ns SRAMS...

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In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Ah, that's a fast SRAM! I'm not sure there is a package compatible one at the next density up.
Cheers
Ed

If you make the land pattern for the 36-pin 512Kx8 CY7C1049, it can be used for the 32-pin 128Kx8 above also. I'm using the 10ns 5V CY7C1049D in my 4Mx8 SRAM modules at http://wilsonminesco.com/WM-1_4Mx8SRAMmodule.pdf .

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Interesting. I never realized that the pinouts work this way. GARTHWILSON, am I correct in assuming that the 36-pin land pattern will work for the 128K chip if the top and bottom rows are not used? That's a good thing to know.

_________________
In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Right. And for SRAM, you don't have to preserve the order of the data lines, or the order of the address lines either. That might help route it on a PCB with fewer layers or vias.

Garth

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Great. Layout accomodates 128K or 512K devices as well as 65C02 or 65C816 via a PLCC socket. I routed out 48 bits using wings layout, although I don't have 2.5V. I doubt any wings use 2.5 anyway. A straight 25-pin header on each side can be soldered in instead for breadboard use.

I have a few tests to run with my oscillators and finetune the BGA process...Almost there.

_________________
In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Great!

Close to the finish line.

_________________
In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut

Small, but perfectly formed!

That looks very, very interesting... I'm definitely interested in one or more of these. Not sure what I'd be using it for, but it looks like another way of getting back into the early 80's (in some ways; in others, definitely not...)

I just bought a NewBrain computer - made about 1982 or so, and in great condition apart from a missing keycap.

rwiker, thanks for your interest.

I will definitely make some extra boards. For my friends here at 6502.org I will make them available at my cost- shooting for $50 with an xc3s200an.

I am thinking of a 'shield' board that snaps on top with VGA, keyboard/mouse, an SD slot, audio out and some kind of joystick/paddle interface (probably a 555-based apple2/commodore style) to turn this into a great retromachine.

_________________
In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut