8-bit CPU control logic: Part 1 

This is the most glorious part. "LDA 14. What does this mean, where does it come from? Well, we're building the computer. We get to decide what stuff means!" For some reason that just puts a beaming smile on my face. And I'm not even building along.

Thanks Ben, now I've blown $300 in breadboards & components, and lost a month of sleep. I keep waking up midnight thinking of chip enables and op codes. 100% worth it

This is a childhood dream come true, except someone else is doing the hard part.

I'm an electrical engineering student and you have cleared up, in less than 30 minutes, material that I've been searching hours on end for, regarding control logic and its implementation in an easy-to-understand manner. I cannot commend you highly enough for this incredibly lucid presentation. Please do not ever take these videos down. As someone else commented, they should be required for electrical/computer engineering students.

LMAO "That zero went over there, I'm not sure if you saw it."

Can't wait to see the 64-bit 24 core version

I feel like this whole series should be required viewing material for all computer engineering students. It covers the whole gamut of topics from software to hardware to architecture design in a detailed but clear way. Thank you so much, Ben Eater, for all the time and work you have put into these videos.

Ben I am at loss words, but will still try. This is by far the most "INFORMATIVE" lecture/demo/tutorial I have seen on how a computer works. Of all the great things this video stands for , the most interesting is the INTUITION it builds. If someone is interested they can watch the entire series,, but even if they go through just this lecture, I am sure one would get insight into a how a computer works. I am also amazed at the efforts and the amount of hard-work that has gone to create this content. If there is any award out there for best teacher, you out to get it. Last but not least, I think this should be required content for every computer engineering student. 👏👏👏👏👏👏👏👏👏👏👏👏👏👏👏

I'm an Computer Science instructor at a community college in California, I have my students build the entire SAP-1 for their Machine Language class. The students seem to really look forward to lab. This will be the 2nd semester that we've incorporated the SAP-1 into the curriculum via the Ben Eater videos. Last semester the students made it to the output register, this semester we are hoping to finish.

The simplicity of explanation is so wonderful. Just from watching your videos, I've been able to connect the dots on how assembly works at a low level, how a cpu processes information, how bit-shifting works, etc. This is fascinating stuff.

For me this is the channel with the most anticipated uploads. Imagine if school classes had been this interesting, how much smarter we would all be. Good job Ben!

This video is beautiful. The content, the didactics, the troubleshooting, the 42 in the end, the lack of audiovisual fillers, the simplicity, etc etc. Thank you very much.

We could run the CE (program counter increment) during cycle 2, shaving a clock cycle off the fetch stage. It doesn't require the bus, so won't collide as long as it's not a counter out cycle.

I just found this playlist the other day and watched through it. Great explanations! I'm very excited for the control logic.

Stopped Netflix immediatly when the notification came. Still there was already 5 likes....ben eater is the best beast in easter....

I just discovered and watched this series. you have a great way of explaining all this complicated stuff. I can't wait for this last bit, that ties it all together. Keep up this good stuff!!

Thank you Ben for all these videos so far! I have watched every of them :) Keep up the good work!

Ben Eater makes it the Best Easter

i nearly screamed when the output didn't update. there was so much anticipation

Can't wait for the next video! Been watching this series breathlessly over the past few days, thank you!

I have learned so much from these videos, I wish I could have seen them when I was in school. Thanks for showing the troubleshooting, I think it is so important in any design.

I watch your videos now, not necessarily because I wanna understand how a CPU work, but because I admire you attention to detail and the way you can communicate something really complex and make it sound that easy. Good job!

The hardware debugging at the end was strangely the most interesting part of this video. Really appreciate you keeping the whole process on screen.

I have been watching your videos today (rainy Easter here in England). I am inspired to build this and have been gathering parts lists from the videos and sourcing components etc. I built my own 8 bit machine back in the day and this will be a journey into even more fundamental architecture. Thank you.

This is such a nice project, really well done and perfectly explained. It reminds me on something similar we did in the digital electronics lab one semester, back in university at the Technical University Berlin. It is so great to see, after so many years, that someone brings the depest root of our digital age to light in such an instructional and well made video. We couldn't use so many breadboards for our "CPU", because in our class we have been groups of only four people each and we ran a bit short on breadboards. We were told to build actually a 4 bit CPU, but I wanted to have an 8 bit one, which I regretted many times, later ;-). We ended up with seven or eight densely packed breadboards and a wiring that looked like an aerial photograph of the amazon basin rain forest. But in the end it worked up to 2 MHz clock frequency. We used an EEPROM as the instruction decoder, in a way like what you would call microcode. The instruction opcode was the address of the "microcode subroutine" in the EEPROM and the bits of the data in the EEPROM represented the different states of the multimplexers etc.. There was a common microcode routine, which increments the program counter by one, put its content on the address bus, load the data into the instruction register and put its content on the address bus of the EEPROM. The LDA command would increase the program counter once more, because we used 8 bit opcodes and 8 bits for data, load its content into the instruction data register, put the value of the instruction data register on the address bus and load the content into register A. And jump to the common "load next instruction" subroutine in the EEPROM afterwards. Other groups went with an FPGA as the instruction decoder and had a hard time even with their 4 bit CPUs. Our EEPROM approach was so plain dead simple and straightforward that, although we have officially been given the choice between FPGA and EEPROM, it felt a little bit like cheating ;-). After this lab, in the time of Z80, 8086 and 68000, I felt like I know what every transistor in my computer is doing, when I was writing a program. Something, I wouldn't dare to say today ;-)

Thank you. I really enjoyed this video. I know that setting up the board took a long time, but it was very educational to see it all happen.

Thank you for such a great explanation. This series is making me put some clarity around assembler with a deeper understanding of modern day computers. Thank you! By the way, I think the best part about the videos series is when something doesn't work and troubleshooting mode commences.

Watching this kind of stuff just puts into perspective how much we take our modern computers for granted.

I really appreciate your methodical approach: step through it manually then think how can we get logic to automate this step, rinse and repeat. It has been a dream of mine to build an 8-bit computer and you make it seem a lot closer.

Saw yesterdays and have been eagerly anticipating.

All the questions which I had on computer science last years have been answered in a while watching this amazing channel! Thanks, Ben.

These videos have blown my mind! Thanks Ben. I got all excited by your videos and bought components to build one myself. Some need to come from China so will take time.

From time to time I come back and rewatch your videos and your amazing teaching skills never stop to impress me!

Love that you include your debugging steps when something goes wrong - helps a lot!

Epic videos man, i cant believe i learned so much about computers from you on youtube, and everything started with me just wanting to discover how software and hardware interact, and I ended up watching hours after hours of your videos. Thanks for this awesome information.

I didn't understand anything from this video, but it's still a pleasure to watch. It makes me feel like a genius.

I just found this series. fantastic!! great work, awesome instructor

This is my favorite episode. Can't wait to build this myself

wow, what an absolutely excellent series. as a self taught (high level) programmer this stuff has always been a bit of mystery to me, so glad i can go through it now for free. Thanks!

just watched every electronics video on this channel in 3 days - and I cannot wait for more :-D

Fantastic! I have long understood how your basic logic works for arithmetic, but was fuzzy on how instruction decoding worked. This is really helpful along those lines.

Thank you sir! Connected the dots of years of questioning

This entire series is by far the most valuable thing I ever found on RU-vid. Thank you so much for putting this out. And not even for me, I'm a seasoned developer, but educational value of those videos can not be calculated, not even by your Turing complete computer ;-)

Thank you for this great work. It is so amazing and I can't stop watching your videos. Such a great job.

I just binge watched the whole series from the start. Fantastic, I tip my hat to you. I don't know how many hours you have put into this thing. I had an idea of how registers, memory and buses worked but seeing it makes a big difference. You deliverance is perfect, the right amount of speed and easy of explaining things. I'm an old fart that recently got into microprocessors and automated controls, I'm absolutely fascinated with electronics. Waiting to see how you are going to control all thise signals, cant wait. Thanks for your time

Great video, now I understand how 1s and 0s turn into instructions. Added bonus was watching you troubleshoot a problem.

frankly, I'm shocked that anyone can demonstrate these concepts so accessibly. I'm a software dev by trade and I have never felt like I understand low-level computing more than I do now. Keep it coming!!!!

Said is very clear and thorough, you can clearly know the CPU architecture and logical operation, hard work

I went through a computer science degree program and I absolutely love your videos. It's so much better than what I learned in university 😂. Especially this part.

Hey Ben, just found out your amazing videos. I was wishing to do something similar but I didn't have and I still do not have enough knowledge like you. Your job is extra amazing and proper, and you become a model for me! Thank you Ben.

8:20 "The beginning of executing any command is a *Fetch* cycle" -- as somebody who's taken countless computer science courses, and learned about the Fetch-Decode-Execute cycle many tens of times, hearing it come up here, for some reason, blew my mind. Never before have I understood something so completely and so instantaneously. The entire reason for the FDE cycle makes so much sense when I've seen you building the CPU from scratch -- how else would it work? Not that I didn't get it before: but now, suddenly, in that moment, I felt like I understood every facet of it. I had an epiphany and it was wonderful. Thank you so very much for these masterful videos!!!

Thanks for the amazing efford you put into your vids. Love your teriffic work. Keep it up!!!

I think you have convinced me to build my own Ben, great series.

Coolest RU-vid series ever!

You're a Wizard, I've always wanted to understand this, it's just never gone into my "memory", thanks to you, I'm now starting to "See" what makes it "Chooch" absolutely brilliant series of videos...Thanks.

Nice explanation how a control unit works in general. Two thumbs up!

Super cool stuff! I've been following along for awhile, but this is going to be the most interesting part for me: implementing the CPU control logic. I've always wondered how it works on this low a level, and most projects are based on existing CPUs that handle the instruction decoding and everything, so you don't quite get to learn what happens "under the hood," getting from the op codes to the control logic. I'm excited! Keep up the good work, my man!

God bless you man. You enlightened me, I am looking all around the web and I found my answers all here. Thank you so much for what you do. This is just incredible. I wish you always be happy and keep on exploring amazing things. Thanks.

One of the greatest videos I saw. And the answer to the “Great Question of Life, the Universe and Everything” at the end makes it EPIC:)

The most amazing computer architecture lecture I have ever seen

So glad I found this! My digital electronics class left me hungry for more of this kind of thing. Can't wait for more :)

Hi I'm a mechatronics student currently on my sixth semester. I have to say your explanation in this video is phenomenal, your way showing how a computer actually runs a programm is intutive to a certain point, you poInt out all the important details and I just love the structure you gave to the computer and how you actually program the commands. Also the way you searched for the issue at the very end from mesuaring highs and lows until you find the specific place where the issue is happening and also looking at the datasheet for the component to see if it's working how it's supposed to I can totally relate to that struggle it's just that my projects have obviously not been this complex lol. Anyway, great video thank you very much for the knowledge you're spreading and greetings from Mexico!

Thanks for this detailed yet easy to understand explanation.

Amazing. I'm glued. Thanks

amazing video as always, thank you for these awesome uploads

I pulled out an old microcontroller I used EE school years ago because my kids are starting to show interest in computer science and I figured it could be a fun way of making simple projects. When trying to start it up and program it, I quickly got overwhelmed with everything I had forgotten or not bothered to learn. This video series revived all that knowledge and memories. When the modules started transfering information on clock pulses, I was just about giddy to the point of tears.

Very cool. I am looking forward to see all parts to come together.

This vedeo tells everything about what's going on inside a computer, from software codes to hardware operations. Great.

I've been watching the whole playlist and basically sitting aghast. And the end of this video was as good as any thriller I've ever seen. On to the next vid. Cheers.

Ben, I can't begin to express how informative and lucid this (and your other videos) are. Too many computer architecture and digital design books gloss over the minutiae of how CPU's are designed and carry out their tasks and your videos explain these details very well. Even though modern CPU architecture is orders of magnitude smaller and more complex, the basics remain the same and these videos are worth a king's ransom if you want to get a real conceptual understanding of CPUs.

That was the best demonstration, of how a computer is hardwired to run software commands. Your manually stepping through the subroutines makes it very clear now how signals are processed. When they say machine language, every machine has its own architecture, so the designer actually hardwires the command codes, then implements the command syntax (software) to use, to execute the hardwired coding. Very good demonstration.

this one is just....... you have a tons and tons of patience,,really nice

Ha, it was pretty great to be following along on the computer I built myself and getting "42" on the first try while Ben was busy troubleshooting. thanks for getting me this far Ben!

Great video! have seen so many small computers videos and always wonder how it works. your explanation is super

you are awesome man!! such person that have this action to build this computer and how it is not good enough you came here to explain to us. you are the man.

Your videos are the best! Good quality and good explanations. Keep it up!

Thank you so much. This is eye opening. I'm new into this kind of logic, so it's a crash course for me. 5.5 GHz are really fast! Thx for slowing it down to realize what happens. All the best for you! 🤗

Thanks ben I have always wanted to know how microcontrollers and cumputers work, and with your explanations, videos and knowladge, I have finally been able to, thaaanks a lot 🙏🏻🙏🏻🙏🏻

been waiting all day for this video!

i wish i could pick your brain for a day. a great breakdown/demo, thanks for sharing

This video is especially fascinating for me. The step-by-step procedure done here is essentially how I would make a program in a high level language (e.g. Python)! That also includes that very interesting "debugging" bit there. I'd literally insert printing statements at various parts of the code to inspect the flow and see where did it start going wrong. It is also very nice to see how each part of the computer work together. Suggestion: I think this video (or kind of an abridged version of it?) would be a very nice introductory video for your 8-bit computer building playlist :D

Amazing video! You are so good at explaining this!

So cool! And you explain it so well!

Great explanation and very clear. Thanks. Waiting for the next :)

Can't thank @Ben enough. Truly a treasure trove. I don't know why I didn't find these videos for this long.

This video helped me understand the difference between assembly and machine code and just how it actually works. What a good feeling of dopamine

Excellent video and expertly explained. Thank you

Greetings from Belgium, that's pure dope , idk why we don't learn this way, graphical approach is so important, easier to learn and so much more interactif, we also feel how deeply you love the tech.

I've been watching this series with my mouth open.. amazing explanation, clear and concise, Thanks! One question though: wouldn't it be nicer to replace the messy control wire jumpers with the tiny switches, even if it's temporary? Again, thanks for the perfect tutorial, it's the first time I've managed to figure out how it all fits..

Thanks a lot for this very nice video ! Very well explained, it's crystal clear !

I work in SW engineering, I know how this stuff works. But I have never seen it explained so f****g well like in this video! Thanks and subscribed!

Very well done series of videos on the fundamentals of solid state. One of the BEST ive seen anywhere. Tubes was all there was when I started doing electronics.. Just think how big a typical cell phone would be even using the peanut sized tubes.. :) Just before I retired I was doing a lot of stuff way beyond the then typical computer stuff. Today the active part of chips are essentially a 2 dimensional layer just a few thousand atoms thick.. Makes me wonder what will happen when they figure out how to stack these layers creating a true 3d chip...

I always wondered how microcode worked on modern CPUs, but after watching your video I feel that I have a much better understanding of what microcode does exactly. The implication is that you could take an EEPROM (or two) and have it drive the control lines, such that it takes the instruction (probably multiplied by some value to divide up the EEPROM into equal regions for the bits that would go to the control lines) and dumps a series of bits into the control lines on each clock cycle, until some signal that the "microcode" for that instruction is complete (perhaps a special signal to the control lines, or just a constant value). Granted you would need some additional control logic just for sequencing the output of the EEPROM(s) to the control lines, including a multiplier for the opcode to feed the start address into the EEPROM and perhaps even some way of sequencing the clock pulses to ensure that the bits from the EEPROM are put on the control lines before all of the other components are clocked after the address being fed to the EEPROM is incremented, but the benefit is being able to reprogram the computer's instruction set on a whim :) awesome series Ben, keep it up!

Thank you a lot for these series! You made my game even better! (I added some of your components into my game!!)

The wiring you do is amazing

I've studied an 8bit made here in our local university. One of the best classes i've taken in my computer science course. Super cool to see It working (and to code It)

it is just amazing !!! thank you very much for these detailed and great videos

Ben , thanks for great explanation and easy for beginner like me to understand.. it is so interesting series.👍

This video just popped up in my feed. I know a needle heads worth about programming, but I was able to follow along for the most part. Very informative.

This was alot of fun to watch, as ive recently got into assembly, which im assuming your instructions were based off. It helped me further understand how asm works