Building a simple 6502 microcomputer

[alkopop79]

GARTHWILSON wrote:

I am slowly working on getting a basic, whole schematic together to post. (I say "slowly" because I've been back to work for the last three months.) It will have 65c02 µP, 32KB ROM, 16KB RAM (using half a 32KB), a 65c22 VIA, a quad NAND for glue logic, and perhaps a serial EEPROM. There will be a note on how to easily add lots more I/O if desired. I started out just modifying the diagram of the computer in the 2nd-to-last picture at http://wilsonminesco.com/6502primer/addr_decoding.html, removing some confusing things that don't need to be that way for the hobbyist, then went on to change the serial EEPROM from Microwire to I²C to get more capacity since it's basically free to do so at this point although we didn't need much for that particular project in 1994, increase the RAM & ROM size, change the I/O connector(s) to be compatible with Daryl's, then realized it was all too much modifying and I really just needed to start over.

I also want to add a pot-pourri page of circuits to interface to different voltage levels, LEDs, LCDs, keypads, I²C, data converters, strings of shift registers, and other things, possibly with code to run those things as shown.

Looking forward to all these additions!

[mkarcz]

Hi alkopop79,

Just dropped in to 6502.org after a long break and notice this thread.
You were looking for some basic diagram of 6502 CPU system?
I got inspired by this project: http://chidesters.org/scott/meadow/Mead ... r_Doc.html
It is a complete minimal 6502 computer with operating system software.
Even though I did not build the exact replica, I adapted Scott's OS to my needs and it proved to be a great help in bringing up my own system.

More on my blog:
[note: I corrected this link because I gave the edit link by mistake, sorry ]
http://6502cpu.blogspot.com/2012/01/650 ... n-and.html

Glad that 6502 has another enthusiast. Good luck with your project.

[whartung]

Perhaps this is the wrong place, but what are the capacitors for that seem to be between the power and ground of each chip? Seems to be a common technique.

[bogax]

whartung wrote:

Perhaps this is the wrong place, but what are the capacitors for that seem to be between the power and ground of each chip? Seems to be a common technique.

Google "decoupling capacitor" or "bypass capacitor"

They're sort of a little electrical surge tank.

In most digital circuits you have in effect a switch to ground
and a switch to the supply connected to the outputs.
One's off and one's is on. When they switch the one that was off
turns on and the one that was on turns off and for a moment
they're both on, sort of shorting the supply to ground.
also there's capacitance on the out put (there's always
capacitance) you're switching that back and forth and it needs
to be charged and discharged and that looks like a momentary short
of the supply to ground. this causes little blips of (relatively) huge
currents. The capacitor supplys that.

Alternatively you can think of the capacitor as a short to ground for
AC (the blips of high current) they short out any noise trying to get
in or out.

[GARTHWILSON]

whartung wrote:

Perhaps this is the wrong place, but what are the capacitors for that seem to be between the power and ground of each chip? Seems to be a common technique.

a little write-up, with links to ap.notes: viewtopic.php?f=4&t=138 (answer starting in 2nd post)

[Tor]

mkarcz wrote:

More on my blog:
http://www.blogger.com/blogger.g?blogID ... 5535358485

Off-topic in a way, but what's with that blogger.com link? It doesn't bring me to a blog, instead it brings me to a google login page.

-Tor

[BigEd]

I think we should try http://6502cpu.blogspot.co.uk/2012/01/6 ... n-and.html and subsequent posts.
Cheers
Ed

[alkopop79]

Bit off topic but can anyone explain me why does the game Minecraft appear in forums about CPUs? Especially homebrew CPUs.

[ElEctric_EyE]

alkopop79 wrote:

Bit off topic but can anyone explain me why does the game Minecraft appear in forums about CPUs? Especially homebrew CPUs.

That topic came up awhile ago.

[alkopop79]

But what's Minecraft? I understand it's a game but why do people use it and what for? What does it have to do with CPUs?

[BigEd]

Think of it as a construction set built on a physics simulator. You can make things which act, in complex ways. So, just like Meccano, TinkerToys or LEGO, there's a possibility of making a mechanical computer, but without the need for expensive materials or physical space. It's a return to Babbage, but without the brass and high accuracy machining.

The original vision of the game is more about an economy simulation, I think: you mine materials from the ground and combine them and trade them. Then you build impressive buildings. But it is very open-ended.

Cheers
Ed

[alkopop79]

Kinda makes sense, thanks!

[alkopop79]

Still a bit off topic but I remember someone mentioning a book about CPUs and how to build them. Since I'm skint and have no money to buy the parts (although Dajgoro kindly offered me his ICs for free!), I started messing with Logisim and decided to build a simple CPU. Had some success but it's still hard to figure out where to start and what makes a processor. Someone recommended a book but I can't remember where....

[BigEd]

This is a good site for many questions we tend to discuss here:
http://electronics.stackexchange.com/qu ... esign-book
and in this case it gets us straight to the book I was thinking you meant:
http://www.nand2tetris.org/

Cheers
Ed

[alkopop79]

BigEd wrote:

This is a good site for many questions we tend to discuss here:
http://electronics.stackexchange.com/qu ... esign-book
and in this case it gets us straight to the book I was thinking you meant:
http://www.nand2tetris.org/

Cheers
Ed

My memory... thanks (again), Ed!