I’m a junior EE student, but I’m still genuinely confused about this, and other answers still haven’t cleared my confusion. How can voltages be manipulated by code in a digital circuit without someone physically closing and opening circuit connections?
In: Engineering
The ones and zeros are voltages. A voltage opens or closes a transistor. This is “physically” closing and opening connections.
You might find it interesting to read a bit about computer architecture, von Neumann and Harvard Architecture.
These building blocks are made out of logic gates, which in turn are made out of transistors. Group the various building blocks together and now you’ve got a primitive ripple carry adder. Group many of these together and you’ve got an arithmetic logic unit. Group those together… Etc etc.
To understand what the actual voltage does it makes sense to just go one abstraction level higher. Keep going until you get to your keyboard.
There is a very handy Java applet that I used to play with as an EE.
https://www.falstad.com/circuit/
Have a look at the sequential logic examples.
Ben Eater has a fantastic series on building a breadboard computer from scratch: https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565dvjafglHU
To answer your question, the first part of each instruction is called the “op code.” This code goes into a decoder which translates the binary value into several control lines. E.g. code 100 (4) turns on the memory address lines, turns on the adder input buffer, and turns off the display input buffer. Think of it like a lookup table of different “recipes” which trigger different actions inside the computer.
Machine code itself is an information that is stored on a memory device. Let’s assume it is stored on RAM. Usually RAM stores 1s and 0s in the form of charged or discharged capacitors. If a charged capacitor is connected to the gate of a transistor – it will conduct. And the other way around with a discharged capacitor.
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