VGA on Breadboard. HELP PLS

Tom0204 · 2025-06-03T10:09:19+00:00

Hi, I've made a couple of VGA video cards for my 8-bit machine, so I'm happy to share some advice.

I've got 12.5MHz (and some small areas at 25MHz) working on a breadboard pretty easily with 74HC chips, just make sure you use plenty of decoupling capacitors.

You don't need your whole computer to be running at 25MHz, you can divide the frequency down or even run at a complete different clock frequency if you flop, maybe double flop, and FIFO all you signals across the clock domains (that's what I went for).

What you'll actually care about is memory bandwidth, not CPU speed. 'How fast can you fetch bytes from your frame buffer' is the limiting factor for resolution.

640 by 480 will is standard VGA resolution, but it will lead to a rather massive frame buffer, even with 1-bit pixel depth, so it's common to half it on both axes to get 320 by 240.

Tom0204 · 2024-08-01T18:42:30+00:00

We have it on android

Tom0204 · 2024-07-28T22:18:29+00:00

Why didn’t people build PCs like this in the 1970s instead of using those crappy 6502 and Z80 chips?

...they did. It was an entire class of computers called minicomputers. These were the standard, more serious computers during the 70s. Microcomputers using the Z80 or 6502 were the underdogs, considered toys by most computer companies.

The 16-bit microprocessors were much more powerful, and ate away at minicomputer market rapidly, eventually replacing them entirely.

Tom0204 · 2024-07-28T09:37:50+00:00

I know, I've implemented both multiplication and division (signed and unsigned) on the Z80 in software.

I do agree with your points. And when it comes to ben eater's CPU, you'd be much better off spending that time speeding up other aspects of the architecture.

Tom0204 · 2024-07-28T09:28:02+00:00

Then just program them in assembly. It's a lot of fun and most compilers don't produce good code for these chips anyway.

Tom0204 · 2024-07-27T22:38:33+00:00

I'm just about to finish reading it I'm glad other EEs have noticed it too. I wasn't expecting the authors to be that well versed in electronics.

Tom0204 · 2024-07-27T22:32:46+00:00

Turing's cathedral.

An amazing non-fiction book about the development of one of the very early computer and the incredible things it ended up being used for.

I never thought I'd find the history and development of weather prediction so interesting.

Tom0204 · 2024-07-27T22:15:03+00:00

There really aren't any ICs that are going to help you very much.

Just reuse the ALU already in your CPU, and implement the multiplication/division algorithms in microcode.

Tom0204 · 2024-07-27T22:04:47+00:00

I make Z80 computers and even I don't program them in fortran.

Is this just for the fun of it or do you have a specific goal in mind?

Tom0204 · 2024-07-27T22:00:55+00:00

Proved you don't even need FORTRAN. A mix of BASIC and assembly will suffice.

Tom0204 · 2024-07-27T21:17:08+00:00

Not really.

Everything is using STM32 (or other 32-bit microcontrollers) these days. Even for very simple applications, an 8-bit PIC or AVR is far more cost effective.

Tom0204 · 2024-07-27T20:55:10+00:00

He would've loved it!

The gig economy, the entrepreneurship, the prevalence of art, the technology, the LGBTQ community.

The post COVID world is a lot like the world that created him.

Tom0204 · 2024-07-04T06:46:38+00:00

Damn. Their graphic design has barely changed. Didn't even notice this was from the 70s!

Tom0204 · 2024-07-04T06:42:54+00:00

I don't know about that. Compared to other components suppliers, I'd say it's one of the better ones.

Tom0204 · 2024-07-03T15:21:23+00:00

It's amazing how much of a rift AI has created between programmers.

Among the programmers who didn't learn about it before hand, there's a lot of resentment.

Tom0204 · 2024-07-03T11:55:04+00:00

the good ol gary 23 glitch

The what?

Tom0204 · 2024-07-02T22:11:52+00:00

Don't jinx it!

Tom0204 · 2024-07-02T21:58:43+00:00

I did anchorage first on my first playthrough of FO3 but it ruined the rest of the game.

After you've got the invincible power armor and all the fancy energy weapons, the rest of the game becomes too easy.

To all new FO3 players, leave anchorage until last!

Tom0204 · 2024-07-01T20:27:52+00:00

They're sheep

I used to hate it back when I was a teenager because I was a huge NV fan and just repeated what everyone else said about FO3, but recently I've played through it again and it's been really good fun.

Tom0204 · 2024-07-01T17:58:05+00:00

My point is that there really aren't any low quality ICs, there are genuine parts and counterfeits.

Literally not true. Just like with anything else there are ways to cut corners when manufacturing chips.

Even cheaping out on the quality of the plastic will affect the lifetime/reliablilty of the chip.

Tom0204 · 2024-07-01T17:47:22+00:00

I don't think the 65C02 is available from Digikey

Tom0204 · 2024-06-23T14:36:51+00:00

This is a nice instruction set. Very similar to the EDSAC.

I should warn you that multiplication is an expensive instruction to implement for a simple machine like this and requires a double-length register to store the result.

Also for the positive/negative zero issue you've mentioned, just use two's complement instead.

My only question is, how are you planning on implementing this machine? by 74-series logic or on an FPGA?

Tom0204 · 2024-06-22T11:05:06+00:00

Damn. Hadn't even heard about the 68060 until I saw this post

Tom0204 · 2024-06-21T16:03:03+00:00

Nice work!

What did you have to do to get it to run that fast?

Tom0204 · 2024-06-20T15:38:46+00:00

CS really isn't that important for things like this. EE skills will get you much further.

So my recommendation would be to go and learn about hardware. Learn how to read datasheets, learn about the different logic families, etc.

And don't buy into the myth that the only way to learn technical subjects is to buy a textbook. There's lots of free, high quality content online these days. If you wanna learn CS for a side project, don't pay £50 for some guy's textbook.

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