logic gates
category: general [glöplog]
Quote:
why is it that i see every tutorial demonstrating how they work show moving parts.
well it's good to know that... and here's a perfect example when you can use it in this way:
http://en.wikipedia.org/wiki/Ladder_logic
hexen: taking a chip apart? better find a chip that has an open part in the middle. this allows you to see the "bondings" (the thin wires running from the pins to the side of the actual chip). important rule of hardware designers: don't cannibalize when you don't have to :)
I wonder why people on pouet only answer to really hardcore topics :|
hexen: At the lowest level we have layers of silicon (wafers), an element which has all its electrons spinning stably around its nucleus. When we dope these wafers with tiny little amounts of other elements with unstable electron orbits (with free electrons or free holes) they become tiny bit of polarized (p or n type). We stick several of these polarized material together so that at their junction current flows (between p and n types).
If you use only a single pair (p with n) current can only flow in one direction. If you use three (p-n-p or n-p-n), many other possibilites occur. When you impose a voltage by external means to one junction, current in the other one will be effected (blocked or allowed). You can then convert this current into voltage. Thus we have a transistor.
At the simplest case you make a digital signal zero (blocking current) if the second signal is zero (low voltage). This makes an AND gate. In practice, many of these transistors are used to build a single gate (more stable more robust gates).
Also for simplicity only NOR or only NAND gates are used which can be combined to produce other gates. This reduces the problem to design only a single gate.
Other physical solutions exist for many other problems but the general idea is the same. Also these transistors do not serve only for digital electronics but for analog control, amplification, filtering etc.
By using the finiteness of the speed of current flow in these transistors, you can combine them to build temporary memory units.
If you use only a single pair (p with n) current can only flow in one direction. If you use three (p-n-p or n-p-n), many other possibilites occur. When you impose a voltage by external means to one junction, current in the other one will be effected (blocked or allowed). You can then convert this current into voltage. Thus we have a transistor.
At the simplest case you make a digital signal zero (blocking current) if the second signal is zero (low voltage). This makes an AND gate. In practice, many of these transistors are used to build a single gate (more stable more robust gates).
Also for simplicity only NOR or only NAND gates are used which can be combined to produce other gates. This reduces the problem to design only a single gate.
Other physical solutions exist for many other problems but the general idea is the same. Also these transistors do not serve only for digital electronics but for analog control, amplification, filtering etc.
By using the finiteness of the speed of current flow in these transistors, you can combine them to build temporary memory units.
We don't tend to use n-p-n or p-n-p (aka bipolar) devices for logic anymore. It's all MOSFET based CMOS logic.
Once you think you've understood the basics of logic gates, move on to a hardware description language like VHDL or Verilog. These are programming languages which can be "synthesized" (meaning compiled, basically) into nets of logic gates.
Yep, there are programs that allow you to layout a chip by putting together p- and n- areas, but those I know of are costly and you won't see them outside a university or hardware company. And it is very tedious to create a chip that way.
So, the closest you can get to designing hardware is with VHDL/Verilog. There are FPGA-boards which you can program with those languages, the cheapest are about 150 dollars and have various I/O ports. I guess it's the point to start if you want to get creative with hardware description languages.
Yep, there are programs that allow you to layout a chip by putting together p- and n- areas, but those I know of are costly and you won't see them outside a university or hardware company. And it is very tedious to create a chip that way.
So, the closest you can get to designing hardware is with VHDL/Verilog. There are FPGA-boards which you can program with those languages, the cheapest are about 150 dollars and have various I/O ports. I guess it's the point to start if you want to get creative with hardware description languages.
Quote:
if i tried to take a computer chip apart. i wouldn't know where to start
Since your average chip these days uses devices and wires a fraction of a micron wide, I think you will have quite a bit of difficulty taking it apart without some veeerrrry expensive machinery :)
trc_wm: wrong. cmos is composed of several mosfets, which are still 2 junction devices (npn, pnp).
wrong 2: bjt is still widely used because of its robustness and speed.
wrong 2: bjt is still widely used because of its robustness and speed.
Yeah, my bad; MOSFETs are made of two p-terminals on an n-type substrate.
I seriously doubt whether BJTs are still in widespread use in logic circuits. Can you point me towards a modern, mainstream, all-BJT logic device?
I seriously doubt whether BJTs are still in widespread use in logic circuits. Can you point me towards a modern, mainstream, all-BJT logic device?
Or two n-terminals on an p-type.. or in a p-well on an n-type substrate.. or ..
<insert random bill gates joke here>
Quote:
.why is it that i see every tutorial demonstrating how they work show moving parts..
In fact they can have moving parts. I learned logic circuits by hooking up magnetic relays.
funny fact: EXOR gate needs seven switching transistors BUT only one relay (guess how?)
haha, imagine building a complex digital system using relays for your logic gates :)
A cpu? clickclickclickclickclick clickclick click click clickclickclickclick click click clickclickclickclickclickcrrrrrrrrrrrrrrrrrrrrrrrrr....
A cpu? clickclickclickclickclick clickclick click click clickclickclickclick click click clickclickclickclickclickcrrrrrrrrrrrrrrrrrrrrrrrrr....
people have done that already. AGES ago...
trc: not being modern and mainstream does not render ttl useless. it's still widely used for interfacing devices. also which cmos device can you use at 100 centigrade? Of course they are being replaced more and more but the situation is far from "It's all MOSFET based CMOS logic". (It's true for processors though).
http://en.wikipedia.org/wiki/7400_series
if you ignore the modernity part.
if you ignore the modernity part.
and yes they are not ttl anymore :)
linde: erm, http://en.wikipedia.org/wiki/Z3_(computer) ?
And guess what, the predecessor (Z1) was even *completely* mechanical, with no electricity whatsoever.
And guess what, the predecessor (Z1) was even *completely* mechanical, with no electricity whatsoever.
lol, that's what i get for being totally oblivious to computer history :P
ahh, zuse! one of the major ass kickers in history. read up on leibniz while you're at it; he made up the binary number system from scratch because he wanted to make a calculator using marbles - in the 17th century! i like to think that if leibniz was alive now, he'd be a popstar, award winning 4k atari 2600 coder and triple phd student at the same time.
skrebbel: WRONG! he's mostly known for baking cookies nowadays :)
