Building a simple 6502 microcomputer

[GARTHWILSON]

You're welcome. I'll keep improving things as I see the need. Actually there's a ton of material I want to add to the site, but it all takes time. I did most of the work on it earlier this year in April through June when I was temporarily out of a job (not officially laid off, but they were temporarily unable to pay me so they didn't give me any work to do either).

The alcohol or degreaser wouldn't be a bad idea, but I've always just been careful how I touch things, and have not had any problems. With the individual pins that I added pictures of, it would make the most sense to use it, since it's kind of hard to avoid touching the long sides of them. Sockets are easier to handle without touching the long sides of the pins with their corners that are essential for a solid, permanent, reliable connection. With the sockets, I just used the paper-towel-beween-pinched-fingers method on them before putting them in the board. It has been so many years since I have used the individual pins that I don't remember what I did.

[BigDumbDinosaur]

alkopop79 wrote:

Garth, your tutorial is probably the best and most exhastive resource about WW. Thsnk you! Just one thing that came to my mind: is it worth to get some alcohol or degreaser to clean the posts?

Isopropanol is a good choice for cleaning, as it leaves no residue, is readily available (sold as denatured alcohol solvent—methylated spirit or "meths" in the UK) and in small quantities, is safe for hobby use. "Degreaser" can mean almost anything, including dangerous chemicals such as acetone or trichloroethane.

Aside from cleaning wire-wrap terminals, use of isopropanol on chip legs can improve solderability or connection quality when the chip is socketed. Do not use rubbing alcohol for any cleaning purpose, as it contains small amounts of oil and other compounds that will leave residue.

[alkopop79]

Thank you gents!

[alkopop79]

Payday in three weeks.... I will read Western Digital's books about the 6502 till then! In a way I'm glad it takes so long to get to the actual building phase. It gives me time to equip myself with theory. Garth's tutorials fascinate me every day. The chapter about propagation delay and the use of different logic families is incredibly insightful.

[GARTHWILSON]

Quote:

I will read Western Digital's books about the 6502 till then!

Just a small note about a common mistake-- it's Western Design Center, at http://www.westerndesigncenter.com/wdc/. (That should help be more successful in finding it.)

[Dajgoro]

GARTHWILSON wrote:

Quote:

I will read Western Digital's books about the 6502 till then!

Just a small note about a common mistake-- it's Western Design Center, at http://www.westerndesigncenter.com/wdc/. (That should help be more successful in finding it.)

I had some issues with that too.
Western Digital is also in the electronic business, as far as i know they make hard disks.

[bogax]

BigDumbDinosaur wrote:

Isopropanol is a good choice for cleaning, as it leaves no residue,

It can be a good choice, but it has a tendency to pick stuff up and
spread it around like paint. If you're not careful you can end up
making things worse.

Also it attacks some plastics.

And my experince is that it does not play nice with (at least some)
saponifiers.

[BigDumbDinosaur]

bogax wrote:

BigDumbDinosaur wrote:

Isopropanol is a good choice for cleaning, as it leaves no residue,

It can be a good choice, but it has a tendency to pick stuff up and
spread it around like paint. If you're not careful you can end up
making things worse.

Also it attacks some plastics.

And my experince is that it does not play nice with (at least some)
saponifiers.

I'm not sure that the average computer hobbyist needs to be concerned about saponification and the reagents involved (e.g., sodium hydroxide, aka caustic soda), unless he accidentally clogs a sink drain with used components. As always, look before you leap, especially with chemicals.

My mention of isopropanol was in regard to cleaning the conductive parts used in wire-wrap construction.

[alkopop79]

Garth, just wanted to comment on your otherwise great article about PCB production. Last year I started a project that involved a microcontroller and multiplexers (never finished but would love if anyone could help me with that, the problem I encountered is trivial for you guys...). It was nigh impossible and impractical to build the thing on breadboard so finally I learnt to make PCBs home. I tried different methods but finally built a UV exposure unit (around $20) and a bubble etch tank (about $10). They worked perfectly. I managed to churn out a single sided board from printing the artwork to the finalised PCB (UV exposure, developing, etching, washing) in 20 mins. I could even make traces for SMD ICs. Even though the initial cost was a bit high since I had to use lots of boards to learn and perfect the method, I got boards way cheaper and faster than as if I ordered them. Never made double sided board and through hole plating but it's viable. For the holes I used a cheap Dremmel knock-off. If I ever build my SBC, I want to build a PCB one too.

[alkopop79]

Some pics of my PCB production line here:

https://picasaweb.google.com/1019225704 ... directlink

[BigDumbDinosaur]

alkopop79 wrote:

Some pics of my PCB production line here:

https://picasaweb.google.com/1019225704 ... directlink

Hey! Those boards look pretty good. But... ...can I get them made in red?

[alkopop79]

BigDumbDinosaur wrote:

alkopop79 wrote:

Some pics of my PCB production line here:

https://picasaweb.google.com/1019225704 ... directlink

Hey! Those boards look pretty good. But... ...can I get them made in red?

We're working on it!

[BigEd]

Nice photos! I've re-posted on g+ with a link back here.

[ChuckT]

GARTHWILSON wrote:

I never put the entire computer on one schematic. There's really no reason to, and there are too many variations it could take.

Your tutorial may be the only tutorial on this site and I'm thankful and really grateful for that.

I think you need one computer on three schematics or three examples on how to build a complete computer because without complete schematics, there are possibly gaps in the learner's understanding.

When I was in college, if I didn't understand something, the instructor wouldn't behave like the school teachers in high school where they repeat the same thing you don't understand as a learner. My instructor in college would teach it differently each time until I understood, it caught on and I learned.

Teaching is more than giving a bunch of facts. Teaching is about presenting facts in a way that people can learn.

You might also have to accept that some people might not catch on for a while and may need three examples to play with until they understand it.

I've seen horrible teachers in High School who said, "If I explained it to you, you would never learn it."

In teaching there is also a difference in telling someone to do something and telling someone how to do it. I had professors in college who refused to teach programming and it could have been better if they gave the students a talk in what they needed to do. Students who had never touched a computer wanted me to help them with their homework and it was too much because the instructor never gave the students the steps to do something.

Today's engineers make a living by taking steps and instructions out of sequential order and they put them in alphabetical order so that only someone who already knows can do something giving techs a job. Steps have to have a linear flow from start to finish.

Please accept this as an constructive help in order to make it better.

[GARTHWILSON]

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.