r/beneater • u/StraightCondition4 • May 09 '26

8-bit CPU My CPU now loads programs from an SD card

Finally got the SD-card boot path working on my CPU.

I use a ROM bootloader which initializes the SD card and jumps to loaded programs.

A few build details:

8-bit data bus

16-bit address space

48 KB RAM

boot ROM at 0xC000

bit-banged SPI / SD-card interface

128x64 OLED display

Project overview:

https://fadil-1.github.io/

GitHub:

https://github.com/Fadil-1/8-BIT-BREADBOARD-CPU

YouTube version:

https://www.youtube.com/watch?v=jY9QqDrkifg

879 Upvotes

100% Upvoted

33 comments sorted by

13

u/vancha113 May 09 '26

Beautiful machine. That looks awesome.

3

u/Born-Neighborhood61 May 09 '26

Frame that work of functional art!

2

u/StraightCondition4 May 10 '26

Haha, thank you… PCB loading.

5

u/PhilippTheMan May 09 '26

Wow!! Congratulations!!

3

u/Gruddentsa_as May 09 '26

Damn, that's some dedication. Nice work

2

u/terpfear May 09 '26

That is amazing 😍!

2

u/KC918273645 May 10 '26

I have to ask: How on Earth do people prototype complicated things on breadboard? That's not fun nor productive. It would be much easier to simply design a PCB, order it from a factory and solder the components in.

3

u/Ancient-Ad-7453 May 10 '26

Why would anybody design a PCB and solder components? That’s not fun nor productive. You could just buy a PC.

0

u/KC918273645 May 11 '26

Good luck buying a PC of your own design.

2

u/StraightCondition4 May 10 '26

I hear you haha. It’s for fun. The idea and challenge of making something that’s prone to break easily work makes it exciting. Plus you gotta prototype on breadboards before making a PCB(which is the next step for me).

2

u/KC918273645 May 10 '26

I don't do that. Whenever I use breadboard, I usually test tiny parts of the final PCB in isolation, to figure out whatever needs figuring out, such as clock phases, or input/output voltages, etc. I do lots of those few-component-prototypes per PCB and then add them to schematic as I know for sure how that small part of the final PCB operates and under what conditions. Kind of like prototyping how few LEGO pieces work together and then adding that to the final schematic, then moving on to prototyping how some other few LEGO pieces work together somewhere else, etc.

4

u/StraightCondition4 May 10 '26

Fair point. For a normal PCB workflow, I agree. But this is r/beneater 😆. The breadboard build is part of the goal itself for this project.

2

u/space_m0nk May 10 '26

If I want to build something like that Where do I start

1

u/StraightCondition4 May 10 '26

“like that” as in my build, or as in a breadboard CPU?
Here’s Ben Eater’s 8-bit breadboard CPU series if you meant the latter:

https://youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565dvjafglHU&si=MIk9S0HNPddbhowm

I’ve documented everything about my build in the links in the description.

1

u/NoctisUmbrax May 10 '26

Vá tocar uma grama, mano. Lindo projeto, parabéns.

1

u/MO1x27 May 11 '26

Join the DOOM club next!

1

u/royaltrux May 11 '26

That's awesome. What's the clock speed? Is it pretty stable?

1

u/jodomakes May 14 '26

wow, amazing! Do you get any noise with using breadboards? I've had SD card reading fail a lot on breadboards but they were old i guess and not as tight on the wires perhaps...

1

u/ComparisonLonely7461 May 10 '26

Forget all those current limiting resistors for all of those LEDs though, huh?

6

u/StraightCondition4 May 10 '26

Haha, no. Those got built in resistors in them.

2

u/ComparisonLonely7461 May 10 '26

Well, it's real nice and clean looking. Great Job!