9 ms·

Build an 8-bit computer from scratch

489 points by kmooney 7y ago

retrac 7y ago
For the last couple years I've been toying with a relay computer design. Only a few prototype circuits have been built, but I do have (several) completed designs. I'm cautiously optimistic... it should be the fastest relay computer ever built, if I actually do build it. I have a whole bunch of reed relays on hand but the boards (and construction time!) are still expensive for a project of that size. What fascinates me is that, even with a full design under my belt which works in simulation, computation remains somewhat magical to me.
- fernly 7y ago
  For historical background, read up on Konrad Zuse[1], who built possibly the first programmable digital computer, using relays, the Z3[2], in 1941. (Neither ENIAC nor Colossus were operational for another couple of years.) There is a much later Zuse design, from discrete transistors, the Z23, in the collection of the Computer History Museum[3]. [1] https://en.wikipedia.org/wiki/Konrad_Zuse https://en.wikipedia.org/wiki/Konrad_Zuse [2] https://en.wikipedia.org/wiki/Z3_(computer) https://en.wikipedia.org/wiki/Z3_(computer) [3] https://www.computerhistory.org/collections/catalog/102669947 https://www.computerhistory.org/collections/catalog/10266994...
zw123456 7y ago
The first time I built a computer from scratch using TTL components was in 1978 for my senior project. I have repeated the effort a couple of times on FPGA's. If you have never tried building your own computer from scratch, you should, it is a great learning experience and also, kind of a lot of fun, I guess if you are a geek which a lot of us on HN are :)
- lnsru 7y ago
  That’s a project many generations of electrical engineering students did in the university in Dresden. It was fun and great experience and admission for final thesis. I think, it’s a must for every electrical engineer since electrical systems barely exist without software nowadays.
- mysterydip 7y ago
  I'm just starting on a project emulating a 4004 system and it's gotten all my geeky brain juices flowing :)
dang 7y ago
Two from 2017: https://news.ycombinator.com/item?id=14450945 https://news.ycombinator.com/item?id=14450945 https://news.ycombinator.com/item?id=14883776 https://news.ycombinator.com/item?id=14883776 Related from a few months ago: https://news.ycombinator.com/item?id=20974405 https://news.ycombinator.com/item?id=20974405 https://news.ycombinator.com/item?id=20614129 https://news.ycombinator.com/item?id=20614129
mrspeaker 7y ago
This series is truly excellent. Ben Eater is a brilliant teacher, and I wish I have has this series growing up - I think I'd be in hardware/electronics now... at the very least, I would have wasted a lot of time tinkering with making my own stuff! I followed along with the clock module and when I was done I had a Matrix style "I know kungfu" moment - it all was crystal clear. And the series doesn't brush over important details (like dealing with flaky inputs that would cause extra clock pulses etc) so even though I still don't know all the math needed for electronics, I'm far more confident in making my own stuff!
- ObsoleteNerd 7y ago
  It’s channels like Ben Eater, Great Scott, Bitluni, and Andreas Spiess that have gotten me into tinkering more with physical electronics lately. It’s such an accessible hobby thanks to the abundance of online information/ideas, cheap components, and simple tools. Plus you learn so much even with the most basic of projects, and considering how much our world now depends on electronics and technology, I think it’s practically useful as well as simply entertaining to learn this stuff.
  - sitkack 7y ago
    Ben Eater, https://www.youtube.com/user/eaterbc https://www.youtube.com/user/eaterbc Great Scott, https://www.youtube.com/user/greatscottlab https://www.youtube.com/user/greatscottlab Bitluni, https://www.youtube.com/user/bitlunislab https://www.youtube.com/user/bitlunislab Andreas Spiess, https://www.youtube.com/channel/UCu7_D0o48KbfhpEohoP7YSQ https://www.youtube.com/channel/UCu7_D0o48KbfhpEohoP7YSQ
    - ObsoleteNerd 7y ago
      Thanks, I should’ve linked them. Will remember to in future.
      - sitkack 7y ago
        No worries, happy to help.
laxd 7y ago
Just started on a fun educational project to emulate a Z80 processor in C. Trying not to look at any existing work, only documentation. Thinking I'll need to expand the project (emulating the rest of an actual, vintage computer) in order to run existing software and get the full kick out of it though. Suggestions? Looking for simplicity as I don't need another forever-project. Edit: asking because there's so many to choose from https://en.wikipedia.org/wiki/Category:Z80-based_home_computers https://en.wikipedia.org/wiki/Category:Z80-based_home_comput...
- swiley 7y ago
  Be careful, if you haven't done this before or done much network programming it's easy to get weird issues with endienness. Check out the ntohs etc. macros. IMO you should try to find a really simple computer to do first. The advantage here is you have other people's software to run which makes for a nice integration test. My first time I did the original apple and had it run the monitor program (which is nice you can just keep adding opcodes going up from the beginning of the program until it works.) For the Z80 I think maybe the ZX80 is the one where it was pretty much just a Z80, a ROM and SDRAM chip and some glue logic?
  - codetrotter 7y ago
    Speaking of simple computers to emulate, Advent of Code 2019 featured an imaginary computer that you gradually implement. (But do note that not all of the days are about said imaginary computer.) I am still catching up with it because I didn’t put so much time into it yet but so far I have completed up to and including day 5 of AoC 2019. For me, this is the first time I have implemented an emulator, and what I like about this imaginary computer is that it is so simple that I was able to build what I have built so far without relying on any external resources. The fun part of it is working through it yourself of course, so even though I am tempted to link to my implementation on my GitHub I will instead only leave a link for AoC 2019. https://adventofcode.com/2019 https://adventofcode.com/2019
  - rantwasp 7y ago
    the one people try at first is CHIP8. Really simple and even with that you can not get it right on the first try
userbinator 7y ago
"You need to enable JavaScript to view this site." I was expecting an interactive 8-bit computer simulation webapp, but all I got was something that could've been several pages on a static site. More disappointingly, it apparently requires a very "modern" browser to view :-( In my experience, to see this sort of anti-accessibility from someone who knows the "low-level" enough to build CPUs successfully is unusual, but unfortunately getting more prevalent. The others I'm aware of, http://www.homebrewcpu.com/ http://www.homebrewcpu.com/ and https://www.bigmessowires.com/bmow1/ https://www.bigmessowires.com/bmow1/ , have far more accessible sites. Edit: looks like others here think accessibility is not a concern anymore. That's really disappointing, especially for low-level stuff.
- SilasX 7y ago
  Maybe tone? If it makes you feel any better, I agree wholeheartedly and appreciate the links to concrete example you think are done right.
- HappyJoy 7y ago
  Take a deep breath and understand that nothing will ever be perfect. If you have that high a standard, download the source, examine it for security and privacy concerns, an proceed if satisfied.
- schwartzworld 7y ago
  imagine finding such amazing content and then being mad that it was built with modern tools. what about the site violates accessibility? JS generated sites should be usable on screen readers. you can violate accessibility, but you can do that without js too
  - madez 7y ago
    Not everything modern is good or positive or even acceptable. JS is not uncontroversial, for good reasons, both technical and political via its influence on society. Lamenting that it is used when there is no need for it seems reasonable to me. The grandparent even made an effort to not just offer destructive criticism but also constructive alternative approaches.
ObsoleteNerd 7y ago
Ben Eater is without a doubt in my top 10 youtubers. His videos are so in-depth and explained in such a great way that I come away learning huge amounts every time he posts. I’m sure a lot of this stuff is basic to people here, but to a software guy, I’ve found his channel invaluable for understanding how computers work at an electronics level and also just wildly fascinating.
- fishingisfun 7y ago
  share some others like him. i would like to explore other youtubers
  - vikramkr 7y ago
    3blue1brown is an amazing intro to mathematics and does an amazing job explaining hairy math concepts with great visuals etc
    - aswanson 7y ago
      Cosign. He's a fantastic explainer.
  - unixhero 7y ago
    Eevblog Smarter every day LEMMINO Socratica Captain disillusion Ahoy Khan Academy Moshix Historia civilis Computerphile jpkiwigeek Ippsec Pydata Deviantollam Lockpickinglawyer Numberphile Strafefox Company Man Accursed Farms Civvie11 ... In no particular order. YouTube is great.
    - exar0815 7y ago
      I would add thesignalpath and mikeselectricstuff to the list. Much more advanced, but very good to learn professional PCB design
  - type0 7y ago
    Applied Science channel is worth mentioning.
deleted 7y ago
[deleted]
barefoot 7y ago
Another great resource is NAND to Tetris (currently auditable on Coursera for free): https://www.coursera.org/learn/nand2tetris2 https://www.coursera.org/learn/nand2tetris2
- clSTophEjUdRanu 7y ago
  This was huge for me. +1
- opnitro 7y ago
  NAND 2 Tetris is great, I don't want to knock it at all, just want to emphasize a difference between it and Ben Eater's content. NAND 2 Tetris explicitly considers most electrical concepts out of scope, and abstracts them away. Eater on the other hand, dives right into them. This isn't a complaint, and it allows NAND 2 Tetris to focus on higher level concerns (such as writing a compiler), but I thought it should be brought up.
  - dinofacedude 7y ago
    I did Nand2Tetris for my computer architecture class. Learned a lot! Definitely recommended. It actually got me into assembly programming as a hobby
deleted 7y ago
[deleted]
jedimastert 7y ago
For anyone itching for more Ben Eater, he's currently working on a series where he takes a 6502-type processor and turns it into a usable computer. Here's the first video: https://www.youtube.com/watch?v=LnzuMJLZRdU https://www.youtube.com/watch?v=LnzuMJLZRdU
transitorykris 7y ago
I’ve been working through Ben’s videos on the 6502 since September. It’s been a highly enjoyable way to relax and learn for me. It’s very easy to go beyond what he’s teaching. There’s so much material out there (6502.org for instance). The most rewarding for me has been taking the basics he gives on address decoding and going beyond it.
TheBiffer 7y ago
There is an iOS version of this at: https://apps.apple.com/ca/app/cpu8/id1448776028 https://apps.apple.com/ca/app/cpu8/id1448776028
Accacin 7y ago
I've been meaning to do through his videos for a long while now and finally over christmas I've managed to binge watch nearly all this series. As a software guy currently doing the Embedded Systems course on edX, Ben's videos have really helped solidify what I've read in the course. Big example was tri-state drivers, after reading about them in the course they hadn't quite clicked, and I searched YouTube and came across Ben's video. He explained the concept so incredibly well, it clicked immediately and I've found it a good companion for the course.
333c 7y ago
I watched the whole video series in the last two weeks. I quite enjoyed it. It suffered from my classes in that Eater actually deals with the minutiae of working with real electricity — debouncing, clock edge detection, and so forth — because he's building his CPU in the real world on breadboards. That was interesting for me to see.
sircastor 7y ago
I just recently found his videos for the 6502. I really wish I'd seen these when I was going through my computing logic class. The text for that was terrible, but these videos explain tremendously well for computers work.
m0xte 7y ago
I am continually impressed that that number of breadboard connections actually works for a lot of people. I never had such luck even with 3M boards.
chrismmay 7y ago
This project looks awesome, and I may purchase Ben's kit to do with my 7 year-old son. My love of computers and software was largely inspired by the 6502 processor. I grew up with the commodore VIC20, C64 and 128 and reading books by Rodnay Zaks in the 1980's. https://en.wikipedia.org/wiki/Rodnay_Zaks https://en.wikipedia.org/wiki/Rodnay_Zaks Perhaps I should look to see if any of my old books are still at my Dad's house. This one is going for nearly $1k on Amazon. Not sure how a book from 1981 can be sold as "new" but wow. https://www.amazon.com/Programming-6502-Rodnay-Zaks-1981-09-03/dp/B01FKX0O8O/ref=sr_1_2?keywords=Rodnay+Zaks&qid=1577631949&s=books&sr=1-2 https://www.amazon.com/Programming-6502-Rodnay-Zaks-1981-09-...
codedokode 7y ago
The description says: > I built a programmable 8-bit computer from scratch on breadboards using only simple logic gates. Sorry, but this is slightly incorrect. First, he is using ready-made adders in ALU which are not "simple logic gates", second he seems to use ROM in control logic which replaces tens or hundreds of logic gates one has to use of they don't have a ROM and a programmer. If I was building a CPU, I would make 1-bit ALU and shift data bit-by-bit to save ICs because 1-bit ALU requires 4-5 simple ICs and 8-bit ALU would require 8 times more and that's too much. Next, I would use 4-bit registers instead of 8-bit because 8-bit register requires 2 ICs and 4-bit register can be implemented with one IC. Also it allows to reduce the number of wires and amount of work to connect them. This makes CPU slower though because it has to access memory twice as often. Also I was surprised to read in comments that in some universities students are designing CPUs as a practical project. Must be interesting.
- kjs3 7y ago
  Translation: I like to crap on other peoples accomplishments. I don't realize that adders are simple logic gates for the people who were actually there when 7400 TTL was a new thing and building ALUs out of adders is one of the oldest ways of building them (unlike "cheating" using a 74181, for example). Or that using PROMs to replace logic is just as old. I propose my "better" way of doing things that unlike the OP I'll never actually do, but I get to crap on him. I'm so disconnected from reality (or went to such a low grade school) I don't know that people actually learn how to build CPUs in school, as opposed to this knowledge being imparted from mystical higher beings directly into CPU architects skulls, or some such. But mostly, I like to crap on other peoples accomplishments.
kjs3 7y ago
I built a Z80 computer for my high school senior project in the early 80s. I got CP/M mostly running; the floppy controller had some bugs I never quite worked out. Pretty much started me on the career path I've taken. I'm building a 68000 system now for fun. I know I'll never really understand my desktop, so I'd like to have at least one computer in the house that I really fundamentally understand.

489 points by kmooney 7y ago

For the last couple years I've been toying with a relay computer design. Only a few prototype circuits have been built, but I do have (several) completed designs. I'm cautiously optimistic... it should be the fastest relay computer ever built, if I actually do build it. I have a whole bunch of reed relays on hand but the boards (and construction time!) are still expensive for a project of that size. What fascinates me is that, even with a full design under my belt which works in simulation, computation remains somewhat magical to me.

fernly 7y ago
For historical background, read up on Konrad Zuse[1], who built possibly the first programmable digital computer, using relays, the Z3[2], in 1941. (Neither ENIAC nor Colossus were operational for another couple of years.) There is a much later Zuse design, from discrete transistors, the Z23, in the collection of the Computer History Museum[3]. [1] https://en.wikipedia.org/wiki/Konrad_Zuse https://en.wikipedia.org/wiki/Konrad_Zuse [2] https://en.wikipedia.org/wiki/Z3_(computer) https://en.wikipedia.org/wiki/Z3_(computer) [3] https://www.computerhistory.org/collections/catalog/102669947 https://www.computerhistory.org/collections/catalog/10266994...

zw123456 7y ago

The first time I built a computer from scratch using TTL components was in 1978 for my senior project. I have repeated the effort a couple of times on FPGA's. If you have never tried building your own computer from scratch, you should, it is a great learning experience and also, kind of a lot of fun, I guess if you are a geek which a lot of us on HN are :)

lnsru 7y ago
That’s a project many generations of electrical engineering students did in the university in Dresden. It was fun and great experience and admission for final thesis. I think, it’s a must for every electrical engineer since electrical systems barely exist without software nowadays.
mysterydip 7y ago
I'm just starting on a project emulating a 4004 system and it's gotten all my geeky brain juices flowing :)

dang 7y ago

Two from 2017: https://news.ycombinator.com/item?id=14450945 https://news.ycombinator.com/item?id=14450945 https://news.ycombinator.com/item?id=14883776 https://news.ycombinator.com/item?id=14883776 Related from a few months ago: https://news.ycombinator.com/item?id=20974405 https://news.ycombinator.com/item?id=20974405 https://news.ycombinator.com/item?id=20614129 https://news.ycombinator.com/item?id=20614129

mrspeaker 7y ago

This series is truly excellent. Ben Eater is a brilliant teacher, and I wish I have has this series growing up - I think I'd be in hardware/electronics now... at the very least, I would have wasted a lot of time tinkering with making my own stuff! I followed along with the clock module and when I was done I had a Matrix style "I know kungfu" moment - it all was crystal clear. And the series doesn't brush over important details (like dealing with flaky inputs that would cause extra clock pulses etc) so even though I still don't know all the math needed for electronics, I'm far more confident in making my own stuff!

ObsoleteNerd 7y ago
It’s channels like Ben Eater, Great Scott, Bitluni, and Andreas Spiess that have gotten me into tinkering more with physical electronics lately. It’s such an accessible hobby thanks to the abundance of online information/ideas, cheap components, and simple tools. Plus you learn so much even with the most basic of projects, and considering how much our world now depends on electronics and technology, I think it’s practically useful as well as simply entertaining to learn this stuff.
- sitkack 7y ago
  Ben Eater, https://www.youtube.com/user/eaterbc https://www.youtube.com/user/eaterbc Great Scott, https://www.youtube.com/user/greatscottlab https://www.youtube.com/user/greatscottlab Bitluni, https://www.youtube.com/user/bitlunislab https://www.youtube.com/user/bitlunislab Andreas Spiess, https://www.youtube.com/channel/UCu7_D0o48KbfhpEohoP7YSQ https://www.youtube.com/channel/UCu7_D0o48KbfhpEohoP7YSQ
  - ObsoleteNerd 7y ago
    Thanks, I should’ve linked them. Will remember to in future.
    - sitkack 7y ago
      No worries, happy to help.

laxd 7y ago

Just started on a fun educational project to emulate a Z80 processor in C. Trying not to look at any existing work, only documentation. Thinking I'll need to expand the project (emulating the rest of an actual, vintage computer) in order to run existing software and get the full kick out of it though. Suggestions? Looking for simplicity as I don't need another forever-project. Edit: asking because there's so many to choose from https://en.wikipedia.org/wiki/Category:Z80-based_home_computers https://en.wikipedia.org/wiki/Category:Z80-based_home_comput...

swiley 7y ago
Be careful, if you haven't done this before or done much network programming it's easy to get weird issues with endienness. Check out the ntohs etc. macros. IMO you should try to find a really simple computer to do first. The advantage here is you have other people's software to run which makes for a nice integration test. My first time I did the original apple and had it run the monitor program (which is nice you can just keep adding opcodes going up from the beginning of the program until it works.) For the Z80 I think maybe the ZX80 is the one where it was pretty much just a Z80, a ROM and SDRAM chip and some glue logic?
- codetrotter 7y ago
  Speaking of simple computers to emulate, Advent of Code 2019 featured an imaginary computer that you gradually implement. (But do note that not all of the days are about said imaginary computer.) I am still catching up with it because I didn’t put so much time into it yet but so far I have completed up to and including day 5 of AoC 2019. For me, this is the first time I have implemented an emulator, and what I like about this imaginary computer is that it is so simple that I was able to build what I have built so far without relying on any external resources. The fun part of it is working through it yourself of course, so even though I am tempted to link to my implementation on my GitHub I will instead only leave a link for AoC 2019. https://adventofcode.com/2019 https://adventofcode.com/2019
- rantwasp 7y ago
  the one people try at first is CHIP8. Really simple and even with that you can not get it right on the first try

userbinator 7y ago

"You need to enable JavaScript to view this site." I was expecting an interactive 8-bit computer simulation webapp, but all I got was something that could've been several pages on a static site. More disappointingly, it apparently requires a very "modern" browser to view :-( In my experience, to see this sort of anti-accessibility from someone who knows the "low-level" enough to build CPUs successfully is unusual, but unfortunately getting more prevalent. The others I'm aware of, http://www.homebrewcpu.com/ http://www.homebrewcpu.com/ and https://www.bigmessowires.com/bmow1/ https://www.bigmessowires.com/bmow1/ , have far more accessible sites. Edit: looks like others here think accessibility is not a concern anymore. That's really disappointing, especially for low-level stuff.

SilasX 7y ago
Maybe tone? If it makes you feel any better, I agree wholeheartedly and appreciate the links to concrete example you think are done right.
HappyJoy 7y ago
Take a deep breath and understand that nothing will ever be perfect. If you have that high a standard, download the source, examine it for security and privacy concerns, an proceed if satisfied.
schwartzworld 7y ago
imagine finding such amazing content and then being mad that it was built with modern tools. what about the site violates accessibility? JS generated sites should be usable on screen readers. you can violate accessibility, but you can do that without js too
- madez 7y ago
  Not everything modern is good or positive or even acceptable. JS is not uncontroversial, for good reasons, both technical and political via its influence on society. Lamenting that it is used when there is no need for it seems reasonable to me. The grandparent even made an effort to not just offer destructive criticism but also constructive alternative approaches.

ObsoleteNerd 7y ago

Ben Eater is without a doubt in my top 10 youtubers. His videos are so in-depth and explained in such a great way that I come away learning huge amounts every time he posts. I’m sure a lot of this stuff is basic to people here, but to a software guy, I’ve found his channel invaluable for understanding how computers work at an electronics level and also just wildly fascinating.

fishingisfun 7y ago
share some others like him. i would like to explore other youtubers
- vikramkr 7y ago
  3blue1brown is an amazing intro to mathematics and does an amazing job explaining hairy math concepts with great visuals etc
  - aswanson 7y ago
    Cosign. He's a fantastic explainer.
- unixhero 7y ago
  Eevblog Smarter every day LEMMINO Socratica Captain disillusion Ahoy Khan Academy Moshix Historia civilis Computerphile jpkiwigeek Ippsec Pydata Deviantollam Lockpickinglawyer Numberphile Strafefox Company Man Accursed Farms Civvie11 ... In no particular order. YouTube is great.
  - exar0815 7y ago
    I would add thesignalpath and mikeselectricstuff to the list. Much more advanced, but very good to learn professional PCB design
- type0 7y ago
  Applied Science channel is worth mentioning.

deleted 7y ago

[deleted]

barefoot 7y ago

Another great resource is NAND to Tetris (currently auditable on Coursera for free): https://www.coursera.org/learn/nand2tetris2 https://www.coursera.org/learn/nand2tetris2

clSTophEjUdRanu 7y ago
This was huge for me. +1
opnitro 7y ago
NAND 2 Tetris is great, I don't want to knock it at all, just want to emphasize a difference between it and Ben Eater's content. NAND 2 Tetris explicitly considers most electrical concepts out of scope, and abstracts them away. Eater on the other hand, dives right into them. This isn't a complaint, and it allows NAND 2 Tetris to focus on higher level concerns (such as writing a compiler), but I thought it should be brought up.
- dinofacedude 7y ago
  I did Nand2Tetris for my computer architecture class. Learned a lot! Definitely recommended. It actually got me into assembly programming as a hobby

deleted 7y ago

[deleted]

jedimastert 7y ago

For anyone itching for more Ben Eater, he's currently working on a series where he takes a 6502-type processor and turns it into a usable computer. Here's the first video: https://www.youtube.com/watch?v=LnzuMJLZRdU https://www.youtube.com/watch?v=LnzuMJLZRdU

transitorykris 7y ago

I’ve been working through Ben’s videos on the 6502 since September. It’s been a highly enjoyable way to relax and learn for me. It’s very easy to go beyond what he’s teaching. There’s so much material out there (6502.org for instance). The most rewarding for me has been taking the basics he gives on address decoding and going beyond it.

TheBiffer 7y ago

There is an iOS version of this at: https://apps.apple.com/ca/app/cpu8/id1448776028 https://apps.apple.com/ca/app/cpu8/id1448776028

Accacin 7y ago

I've been meaning to do through his videos for a long while now and finally over christmas I've managed to binge watch nearly all this series. As a software guy currently doing the Embedded Systems course on edX, Ben's videos have really helped solidify what I've read in the course. Big example was tri-state drivers, after reading about them in the course they hadn't quite clicked, and I searched YouTube and came across Ben's video. He explained the concept so incredibly well, it clicked immediately and I've found it a good companion for the course.

333c 7y ago

I watched the whole video series in the last two weeks. I quite enjoyed it. It suffered from my classes in that Eater actually deals with the minutiae of working with real electricity — debouncing, clock edge detection, and so forth — because he's building his CPU in the real world on breadboards. That was interesting for me to see.

sircastor 7y ago

I just recently found his videos for the 6502. I really wish I'd seen these when I was going through my computing logic class. The text for that was terrible, but these videos explain tremendously well for computers work.

m0xte 7y ago

I am continually impressed that that number of breadboard connections actually works for a lot of people. I never had such luck even with 3M boards.

chrismmay 7y ago

This project looks awesome, and I may purchase Ben's kit to do with my 7 year-old son. My love of computers and software was largely inspired by the 6502 processor. I grew up with the commodore VIC20, C64 and 128 and reading books by Rodnay Zaks in the 1980's. https://en.wikipedia.org/wiki/Rodnay_Zaks https://en.wikipedia.org/wiki/Rodnay_Zaks Perhaps I should look to see if any of my old books are still at my Dad's house. This one is going for nearly $1k on Amazon. Not sure how a book from 1981 can be sold as "new" but wow. https://www.amazon.com/Programming-6502-Rodnay-Zaks-1981-09-03/dp/B01FKX0O8O/ref=sr_1_2?keywords=Rodnay+Zaks&qid=1577631949&s=books&sr=1-2 https://www.amazon.com/Programming-6502-Rodnay-Zaks-1981-09-...

codedokode 7y ago

The description says: > I built a programmable 8-bit computer from scratch on breadboards using only simple logic gates. Sorry, but this is slightly incorrect. First, he is using ready-made adders in ALU which are not "simple logic gates", second he seems to use ROM in control logic which replaces tens or hundreds of logic gates one has to use of they don't have a ROM and a programmer. If I was building a CPU, I would make 1-bit ALU and shift data bit-by-bit to save ICs because 1-bit ALU requires 4-5 simple ICs and 8-bit ALU would require 8 times more and that's too much. Next, I would use 4-bit registers instead of 8-bit because 8-bit register requires 2 ICs and 4-bit register can be implemented with one IC. Also it allows to reduce the number of wires and amount of work to connect them. This makes CPU slower though because it has to access memory twice as often. Also I was surprised to read in comments that in some universities students are designing CPUs as a practical project. Must be interesting.

kjs3 7y ago
Translation: I like to crap on other peoples accomplishments. I don't realize that adders are simple logic gates for the people who were actually there when 7400 TTL was a new thing and building ALUs out of adders is one of the oldest ways of building them (unlike "cheating" using a 74181, for example). Or that using PROMs to replace logic is just as old. I propose my "better" way of doing things that unlike the OP I'll never actually do, but I get to crap on him. I'm so disconnected from reality (or went to such a low grade school) I don't know that people actually learn how to build CPUs in school, as opposed to this knowledge being imparted from mystical higher beings directly into CPU architects skulls, or some such. But mostly, I like to crap on other peoples accomplishments.

kjs3 7y ago

I built a Z80 computer for my high school senior project in the early 80s. I got CP/M mostly running; the floppy controller had some bugs I never quite worked out. Pretty much started me on the career path I've taken. I'm building a 68000 system now for fun. I know I'll never really understand my desktop, so I'd like to have at least one computer in the house that I really fundamentally understand.