Universal Serial Bus (USB)#
The USB is serial bus commonly used in computers.
Overview#
| 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 |
| Spec | |
|---|---|
| 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.
Pinout#
| 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:
- Diff "0" (D- Hi, D+ Lo): Idle Low Speed Device
- Diff "1" (D- Lo, D+ Hi): Idle Full Speed Device
All further communication is initiated by the host.