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Universal Serial Bus (USB)#

The USB is serial bus commonly used in computers.


Standard Speed Current
USB 1.0 (1996) 12 Mbit/s 100 mA
USB 2.0 (2000) 480 Mbit/s 500 mA
USB 3.0 (2008) 5.0 Gbit/s 900 mA
USB 3.1 (2013) 10 Gbit/s
USB 3.2 (2017) 20 Gbit/s

Maximum devices: 127. Cable length: \(< \SI{5}{m}\)

USB Connectors

USB 2.0#

Pin Signal Color Meaning
1 VBUS Red Vdd
2 D- White Inverted Signal
3 D+ Green Signal
4 GND Black Ground
Speed 480 Mbit/s
Voltage 5.0 ± 0.25 V
Current 100mA, 500mA, 5A
Length < 5 m

The practical speed is 280 Mbit/s due to bus access constraints.


Standardstecker A / B
Pin Color Signal Description
Shell n.a. Shield Schirmgeflecht
1 Red VBUS +5 V
2 White D− Data USB 2.0, differential Pair −/+
3 Green D+
4 Black GND Ground

USB 3.0#

Pin Color Signal name Description
A connector B connector
Shell N/A Shield Metal housing
1 Red VBUS Power
2 White D− USB 2.0 differential pair
3 Green D+
4 Black GND Ground for power return
5 Blue StdA_SSRX− StdB_SSTX− SuperSpeed transmitter differential pair
6 Yellow StdA_SSRX+ StdB_SSTX+
7 N/A GND_DRAIN Ground for signal return
8 Purple StdA_SSTX− StdB_SSRX− SuperSpeed receiver differential pair
9 Orange StdA_SSTX+ StdB_SSRX+
The USB 3.0 Powered-B connector has two additional pins for power and ground supplied to the device.
10 N/A DPWR Power provided to device (Powered-B only)
11 DGND Ground for DPWR return (Powered-B only)

The Protocol#

Idle State#

When any client device is connected it switches into one of two idle states:

  1. Diff "0" (D- Hi, D+ Lo): Idle Low Speed Device
  2. Diff "1" (D- Lo, D+ Hi): Idle Full Speed Device

All further communication is initiated by the host.