Building a simple 6502 microcomputer

[alkopop79]

BigEd wrote:

Good tips!
How have you labelled the pins/posts?
Cheers
Ed

Paper strips glued to the board with Pritt Stick. https://docs.google.com/file/d/0B5VgMsm ... gwQ28/edit

[alkopop79]

BigDumbDinosaur wrote:

alkopop79 wrote:

- wire wrap (WW) might be more expensive than soldering but fast, reliable and can connections can be easily un-done. The tool can be purchased from Farnell and way cheaper than on Ebay ( http://uk.farnell.com/jsp/search/produc ... f-00001000 ).

That tool appears to be the same one I have, which I bought a long time ago.

The only problem I had with this tool is that it used to break the wires in the beginning. I think I had to 'break it', like a pair of new leather boots. After 30+ wrapping the sharp bits had been abraded and had no problem since then.

[alkopop79]

Somone noted in a blog that WW is like meditation. I totally agree. You don't need the soldering iron, only a spool of kynar and the tool and it can be done while watching a movie. I already miss WW-ing. Gotta find an other SBC to build...

[alkopop79]

Also, I recommend using WW headers to distribute the power: http://spiratronics.com/product-39395.html One post is not enough to wire all the ICs to so I used four pairs (VCC+GND) of headers placed at different points of the board, all connected to one pair. Do not daisy chain!

[Dajgoro]

alkopop79 wrote:

Gotta find an other SBC to build...

I have a 6802(my sbc was supposed to run with it, but i changed my mind for the 6502), and no plans for it.

[alkopop79]

Gentlemen, is there anyone who could burn EEPROM for me in the UK? I've been struggling with a home made contraption and doesn't seem work properly.

[BigEd]

If you mean a 28-pin DIP like the BBC micro's ROMs, I can probably help.

[alkopop79]

Indeed it's a 28 pin DIP however it only needs 5 volts for programming. Dajgoro is helping me debugging the EEPROM programmer contraption but if it fails I'll need your help. Thank you!

[alkopop79]

I read somewhere that ROMs have to erased before writing. I wonder if that stops me from being able to write my EEPROM? I checked the datasheet and the erasing waveform looks identical to the writing one except the erasing pulse takes longer (10ms as opposed to the 100ns of writing) and the output enable pin is 12 volts. Since I have the MCU and the breadboard set up for writing I wonder if I can just use a buffer/driver IC with 12V VCC? The input would come from the MCU, the output would go to the OE of the EEPROM. Would that work? Or should I just use a transistor to switch the 12V for erasing?

[Dr Jefyll]

Quote:

I wonder if I can just use a buffer/driver IC with 12V VCC? [...] Or should I just use a transistor to switch the 12V for erasing?

These both sound like workable options, AP. As long as the voltage & current spec's are satisfied then the EEPROM won't know the difference.

Just remember that applying 12 volts could be disastrous if not done properly. If you're at all uncomfortable it might be best to share your proposed circuit (and the EEPROM data sheet) with us before you proceed.

have fun!
Jeff

[leeeeee]

Quote:

I read somewhere that ROMs have to erased before writing.

EEPROMs shouldn't need erasing before writing. You can erase the whole device in one go, having applied 12V to /OE and usually using a software code, but you don't need to.

You should be able to rewrite any or all of the bytes in a page in one go using the write command. One thing to remember though is that no read will work while a write command is active, all you will get is the write status until the write is complete.

Lee.

[alkopop79]

I just realised, the Atmel EEPROM I've been trying to program is incompatible with the UK101 because of the difference in pinouts. So I will have to purchase an old 28 pin EPROM/EEPROM. BigEd, once I get paid I will need you kind help! Thanks in advance!

[Dajgoro]

What eeprom do you have, what model is it?

[alkopop79]

Atmel 28C64B

[Dajgoro]

Ah.
That is the IC that I was suggesting that I might send it to you, but I also told you that it wouldn't work, since it is too small (8k).
What you need is a 28C256 (32k), or bigger, maybe some 29xxxx IC would suit you.
But again, you should be able to program the one you already have (except if you were rewriting it a few times while programing, since you tried to write a bigger file that it actually fits)...

http://www.ebay.com/itm/1PCS-XICOR-X28C ... 3cbe363a1c
Many of you are discouraged by the look of IC that are sold on ebay, but I never had issues with them.