How does input data travel through a USB cable?
How does the data physically travel trough the USB? Electrons? Electron pulses? I can understand how electrical energy in a cable travel by means of electrons, but computer data??
I understand that a USB cable exist of 4 wires (2 for data travel, 1 for energy to power a device and 1 that act as a ground wire).
So are there a difference in what actually travels through the four wires?
May 26th, 2010 at 12:47 am
Digital signalling over a cable involves the constant changing of an electrical voltage.
Changes in voltage indicate 0 or 1 (high voltage to low = 0, low voltage to high = 1).
You’re correct on the USB cable wires.
Data is sent through the data pins using digital signalling. The power pin supplies 5V power to the device.
May 26th, 2010 at 1:23 am
I didn’t fully understand [1], so it probably doesn’t answer your question.
The electrons can change the state of a receiving device between 0 and 1 – bingo, binary communication. That’s how! It’s just that it works so fast and small, that we struggle to perceive it like that on our human scale and speed.
May 26th, 2010 at 2:22 am
OK, the 4 wires are in 2 groups.
power and ground – to supply power to equipment at the other end.
eg the LED in the mouse, the motor in the diskdrive.. .the Web Camera
The two signalling wires, are in one of two states (DIfferential states)
state 0
A wire : +ve
B wire : -ve
so that current flows from “A to B”
and state 1< A wire : -ve B wire : +ve so that current flows from "B to A" You then change from 0 to 1, to show the data you want to send. as fast as you need/USB standard says it should. As for electricity: All electricity is electrons flowing down a wire " current" the faster, the higher the current (Amps). The Voltage is the ammount of push to make the flow happen. compare to water flowing. Amps is how much water is actually flowing past where you are standing. Voltage is how high the lake is feeding the stream. (and resistance is how wide/narrow the stream is.. if it is narrow but being pushed hard.. more water will flow... or wide and being pushed slowly could be the same amount). Its all electrons, because it's all electicity. It's a matter of how much, and whether your need lots of power (amps) - the power pair or just to know if you want to push in one direction or the other (knowing is enough, you don't actually need to move any real power to signal) - the signalling pair.