Hacker News Reader

Hacker News

Comment by mrob | Hacker News Reader

Parent Full thread

mrob

>Ben Eater is building a VGA card from discrete components

From 7400 series devices, which are very simple integrated circuits by modern standards, but still integrated circuits.

View on HN

"From 7400 series devices, which are very simple integrated circuits by modern standards"

So it's clear, a 74xx is just a bunch of NAND gates. Nothing at all higher level than that.

Among my group of SW engineering circle, we had a running joke that software is a series of 1s and 0s, it is the sequence that is important.

Although NAND gates are universal gates (any combinatorial boolean logic function can be built from nothing but NAND gates), in practice it's usually more space efficient to use a mixture of different gates.

And usually more power-efficient and faster in execution speed.

Except they're not. He's using 74161 counters; that's a MSI device, not just primitive combinatorial logic and flip flops.

Ahh, good catch. I was distracted with the 7400 description. Though a 4 bit counter isn't terribly high level either.

Counters are a series of flip-flops anyway, right? And a few latches for reset and load.

https://easyeda.com/normal/74161X2-4qkCwOIZh.png

To be fair, it's almost impossible to build anything out of fully discrete components these days. If you use a TO series transistor, you could argue those are also ICs and vacuum tubes/relays aren't cheap or too easily accessible.

Transistors in individual packages are called discrete components. Even if they use the same technology as ICs, they're still discrete. You can certainly build useful analog and power circuits with only discrete components. Somebody even made a CPU from them [1] which was a much bigger circuit than TFA's IC video card will be so it's worth distinguishing truly discrete from simple ICs.

[1] https://monster6502.com/

Chip photography site zeptobars.com has some photographs of modern transistors, and while some have interesting geometry, I didn't see anything that I'd consider an integrated circuit, i.e. something that would be drawn as more than a single transistor symbol on a schematic.

https://zeptobars.com/en/read/NXP-PMST3904-NPN-BJT

https://zeptobars.com/en/read/NXP-MMBT3904-npn-bjt

https://zeptobars.com/en/read/NXP-2N7002-TrenchMOS-N-Channel...

There are some "discrete" transistors with built-in ESD protection, e.g. NCV8440A, but those are unusual, and under normal operating conditions they work just like a normal transistor so I'd still count them as discrete components.

Similar to the difference between asm (discrete), C (low level logic ICs), and Python (ATmega).

Reply on news.ycombinator.com