TTL Computer

[@ColonelTux]

Well done! Excellent video giving a high-level overview of the project and its execution.

[@eskwadrat]

I am 50+ EE professionally designing electronics for various embedded systems used in controls for consumer, automotive to medical products. My career jump started in early 90s when I developed handful of control based on 8051 microcontroller. Later complexity of my designs progressed until now when I mostly design around SoCs and FPGAs, but sometimes simple MCU comes handy. Fast forward 35 years later today I cannot shake off that desire to built 8051 core based on TTL series. That would allow me to make full circle before I am old too much to endavour on such interesting project. Your video is another proof and inspiration I can pull it off. Thanks for the video

[@danapeters]

Great, glad you found this inspirational. I found that Logisim was invaluable. I doubt I would have completed it without simulation. And custom PCBs are quite affordable, so now is a good time to tackle such a project.

[@CATech1138]

impressive..been wanting to do this for 10 years or so... PS...good job on the video too....nobody would believe how hard it is to make a decent video

[@shomazfiddle]

Great video and project! I'd love to see some more software running on it.

[@pietpaaltjes7419]

Impressive project. Reminds me of the Gigatron ttl computer.

[@GothGuy885]

Beautiful! really enjoyed your video, thanks! 😀

[@Jojo3Trek]

This is brilliant work! Also, excellent presentation and walkthrough. 🖤

[@MatsEngstrom]

Autorouted and no decoupling caps whatsoever and it still works at 3MHz. Does it even have a properly routed power distribution bus with wider tracks? It clearly shows that the old LS-TTL is super resilient and can handle the most severe environments. Nicely done.

[@danapeters]

The power distribution tracks were 18 mil, and all the other tracks were 6 mil wide. Also, I soldered axial 0.1 uF decoupling capacitors diagonally across the power pins of each chip on the bottom of the PCB. This avoided having to worry about decoupling when routing the board. I learned the hard way that decoupling was important because I accidentally omitted decoupling from just 2 chips on the prototype, and it caused problems. I used 74HCT so I didn't need to worry about fanout limitations. Thanks for your interest, I'm glad to get so many comments.

[@MatsEngstrom]

@@danapeters Ah, that definitely makes more sense. On solderless breadboards I sometimes solder the decoupling caps across the IC itself instead of just hooking them up across the power rails which gives a lot less loop area/distance. Putting them across on the bottom of the PCB is smart (and it actually make the boards look better from the top with just the ICs showing). ^__^. For me routing is meditative and I can spend days of my free time routing, ripping up, moving a few ICs, route again and repeat until done. But I realise that most people (rightly) just want to get to the finished product. You deserve many comments, it's a nice relatively advanced design. BTW - have you planned any other "top" boards for it? Maybe make it more like a 1970/1980s trainer board?

[@TomLeg]

Some routing is simpler than other parts. If you route power supplies, and traces which remain within a limited region, the rest of the route becomes simpler. Some autoroutes allow you to select a set of pins, which it will route. Handling small regions is always fairly quick, and if a problem requires re-doing an earlier segment, a human will perform better than a matching. It isn't actually THAT hard, you'll learn it quickly enough, considering what you've already achieved.

[@NANDOFFDataRecovery]

impressive work. well done.

[@ElectronicFanArm]

Simply beautiful excellent job

[@pablovicentico]

This is a mega cool project!

[@martinhovorka69]

We used computers like this in the 90s at university for Assembler programming, but of course they used the i8080.

[@fisc_rl]

That's awesome! Someone should compress this down into a single chip. I could see that being a big hit.

[@briancampbell179]

Really? What would you use that for? Why would anyone want a computer fits in the palm of your hand?

[@mikemilner8080]

As the history lesson should have made clear, current SoCs with ROM, RAM, and clock speeds in excess of this machine are available. Digikey sells one for $8.42 that has 512KB of flash (vs 16K), 64KB of RAM, and runs at 24MHz (vs. 3MHz). It also includes I/O pins more sufficient to handle the input and output of the TTL machine. Of course, if you just wanted a calculator, you could try to find an Intel 4004 - the first microprocessor - developed specifically to provide a single chip processor for, you guessed it, a calculator. It was cheaper and more versatile than a dedicated set of chips that the customer thought necessary.

[@briancampbell179]

@@mikemilner8080 my understanding was that the 4004 was developed for NCR cash registers.

[@stevetodd7383]

Erm, what on earth would they do that for? There a two streams of thought about building retro-computers. The first, like this, says wouldn’t it be neat if I could build my own computer entirely out of TTL chips. They aren’t trying to replicate an existing design and there’s almost no software available for them. The second is that there is all this old software available, how do I run it on modern hardware? This latter category results in either software emulators or FPGA cores (for those not in the know, an FPGA is a chip with lots of logic resources on board, but initially nothing connected. You can programmatically wire them together using a flash rom configuration, generated using software on a desktop PC. This, when it comes to a complete system, is referred to as a core).

[@stevetodd7383]

@@mikemilner8080heck, that’s an expensive example. The Raspberry Pi Pico 2 has 4 CPU cores (two of which are available at once admittedly), runs at 150MHz, has 520K of RAM and 4MB of ROM for £5. ESP32 based dev boards or STM32s can be had for under £2.

[@rupertmurdoch469]

Beautiful design!!!

[@mikemilner8080]

What architecture did you pick? Von Neumann or Harvard? Instruction set - RISC or CIS? There are lots of levels of detail and design choices. Would love to have school kids exposed to this level to demystify the cell phones they all take for granted. Small nit - technically TTL uses bipolar transistors while it appears you used CMOS which is based on field effect transistors. The 7400 series started as pure TTL and added 7 variants from 1966 to 1982; CMOS equivalents first appeared in 1968 and have evolved through at least 40 variants since.

[@danapeters]

You are correct, even though I called this a "TTL computer", I actually used 74HCT chips to avoid fanout issues. These are MOS, not TTL, although they are TTL-compatible. The 74181 ALUs I'm using really are TTL chips. As for architecture, it is inspired by the OSIC (one instruction computer) architecture. But it supports different arithmetic/logical operations, branch conditions, and addressing modes, so I don't know if it really is OSIC or not. I'm calling it QSIC (for Quasi Single Instruction Computer). I intend to make another video on this, so stay tuned!

[@inscruptabletv9260]

really cool project! Keep it up

[@scottfranco1962]

Nice, but I don't see the advantage vs. doing it in an FPGA. I did a 8080 design in a Xilinx FPGA.

[@jamesross3939]

Very cool!

[@alexloktionoff6833]

Great! What is the architecture? What is the performance per kilohertz? Battle Royale could be nice to watch too...

[@danapeters]

The TTL computer was inspired by kzbin.info/www/bejne/oIO9daGbqc96q9E about the One Instruction Set Computer (OISC) architecture. But I've added multiple arithmetic/logical operations, branch conditions, and addressing modes, so I'm not sure if it qualifies as a true OISC. I hope to make another video about this.

[@bertkoerts3991]

Did you find software to move your design from Logisim to EasyEDA? Does that even exist? Thanks, I’ll be following! 😊👍🇳🇱

[@danapeters]

Interesting idea... I didn't look for such software because I assumed that it did not exist. There are many different parts you can select in EasyEDA, so the software would need to specify a particular part, and then you'd have to modify it later if you wanted a different part. Still, that would likely be easier than redoing it in EasyEDA from scratch.

[@gregorymccoy6797]

In the future you will want to add decoupling caps on each and every TTL chip. Curious, what is the total power draw for all those hungry chips? I think your project is beautiful. Okay read all the comments now....you DID add the caps. Awesome.

[@drivers99]

I saw in another comment he did add them diagonally across the power chips on the bottom of the board

[@danapeters]

Yes, it is true that I cheated and just soldered decoupling capacitors diagonally across the power supply pins of each chip on the bottom of the board, so that I didn't have to worry about routing those connections. This also guarantees the shortest possible connection for decoupling. The TTL chips take very little power, because I cheated here too and used the 74HCT variant to avoid fanout concerns. But the computer still needs lots of power because of the 7-segment LEDs, which I'm driving fairly hard at 20 mA. So if all segments are on, that would be 8 x 7 x 20 = 1120 mA.

[@drivers99]

@@danapeters I don’t think it’s cheating! Interesting point about the LEDs. I started getting parts for a project and it was the first time I considered the efficiency of the LEDs and what resistors I should really use to keep the current down because I was driving everything from Raspberry Pi Picos and the current was pretty low. I even considered whether to use transistors to drive them. It’s a lot more soldering adding all these components though.

[@DumbledoreMcCracken]

How are floating point numbers represented?

[@danapeters]

This basic calculator software uses fixed point rather than floating point to represent numbers. The integer part uses 32 bits, and the fractional part uses 32 bits. So it takes four 16-bit values to represent a number. This gives sufficient precision and range for an 8-digit display.

[@DumbledoreMcCracken]

@@danapeters thank you; I don't think I have ever heard of that scheme previously.

[@VladoT]

Do you have plans to make this as a complette kit?

[@danapeters]

I intend to publish the design on a web site, including all the files needed to build it if you want to. I'll need to clean some things up before I do that.

[@VladoT]

@@danapeters Great, it looks promising especially if it runs at higher clock speeds.

[@user-folk1987]

Hi! When i find link to you website?

[@danapeters]

I still have to clean up the files before publishing them, so no web site yet, but I intend to do this soon. Thanks for your interest!

[@rbyt2010]

What?? Not wire wrapped?

[@danapeters]

I considered wire-wrapping. But I wanted to learn how to make a PCB, since it is surprisingly inexpensive. Probably cheaper than wire-wrap sockets!

[@rbyt2010]

@@danapeters ah, sorry. Thought this was a retro thing. Back when we designed and shipped cpus from TTL and ECL we used ww. You’re right! Pcb’s are really inexpensive and the tools now are great :)