Universal Serial Bus (USB)

USB

Universal Serial Bus (USB)

General specifications
Length	2–5 m (6 ft 7 in–16 ft 5 in) (by category)
Width	12 mm (A-plug),[1] 8.45 mm (B-plug); 7 mm (Mini / Micro-USB)
Height	4.5 mm (A-plug),[1] 7.78 mm (B-plug, pre-v3.0); 1.5–3 mm (Mini/Micro-USB)
Hot pluggable	Yes
External	Yes
Cable	4 wires plus shield (pre-3.0); 9 wires plus shield (USB 3.0)
Pins	4: 1 supply, 2 data, 1 ground (pre-3.0); 9 (USB 3.0); 11 (powered USB 3.0); 5 (pre-3.0 Micro-USB)
Connector	Unique
Electrical
Signal	5 volt DC
Max. voltage	5.00±0.25 V (pre-3.0); 5.00+0.25-0.55 V (USB 3.0)
Max. current	0.5–0.9 A (general); 5 A (charging devices)
Data
Data signal	Packet data, defined by specifications
Width	1 bit
Bitrate	1.5/12/480/5,000/10,000 Mbit/s(depending on mode)
Max. devices	127
Protocol	Serial
Pin out
The standard USB A plug (left) and B plug (right)
Pin 1		VCC (+5 V, red wire)
Pin 2		Data− (white wire)
Pin 3		Data+ (green wire)
Pin 4		Ground (black wire)

Types of USB connector left to right (ruler in centimeters): Micro-B plug, UC-E6 proprietary (non-USB) plug, Mini-B plug, Standard-A receptacle (upside down), Standard-A plug, Standard-B plug

Micro A USB

Micro B USB

USB Mini A (left) and USB Mini B (right) plugs

Host and device interface receptacles[edit]

Connectors (receptacles and plugs) mating matrix is displayed below. As a note, the assignment of functions (V_CC, D+, D−, GND and ID) to pin numbers marked below is mostly consistent, with the exception of Mini and Micro connectors. When compared to standard-sized connectors (Type-A and Type-B), Mini and Micro connectors have their GND connections moved from pin #4 to pin #5, while their pin #4 serves as an ID pin for the On-The-Go host/client identification.^[64]

USB connectors mating matrix

Receptacle (images not to scale)	Plug (images not to scale)
	Yes	No	No	No	No	No
	No	Yes	No	No	No	No
	No	No	Deprecated	No	No	No
	No	No	Deprecated	Deprecated	No	No
	No	No	No	Yes	No	No
	No	No	No	No	Yes	Yes
	No	No	No	No	No	Yes

Cable plugs (USB 1.x/2.0)[edit]

USB cables exist with various combinations of plugs on each end of the cable, as displayed below. Notes from the section above apply here as well.

Plug (images not to scale)	Plug (images not to scale)
	Non-standard	Non-standard	Non-standard	Yes	Yes	Yes
	Non-standard	No	No	Deprecated	Deprecated	Non-standard
	Non-standard	No	No	Non-standard	Non-standard	Yes
	Yes	Deprecated	Non-standard	No	No	No
	Yes	Deprecated	Non-standard	No	No	No
	Yes	Non-standard	Yes	No	No	No

USB 3.0 Micro-B plug

Micro-B USB 3.0 plug

1. Power (V_BUS)
2. USB 2.0 Data− (D−)
3. USB 2.0 Data+ (D+)
4. USB OTG ID pin
5. GND
6. USB 3.0 Transmit− (SSTx−)
7. USB 3.0 Transmit+ (SSTx+)
8. GND
9. USB 3.0 Receive− (SSRx−)
10. USB 3.0 Receive+ (SSRx+)

USB 1.x/2.0 standard pinout

Pin	Name	Wire color	Description
1	VBUS	Red (or Orange)	+5 V
2	D−	White (or Gold)	Data−
3	D+	Green	Data+
4	GND	Black (or Blue)	Ground

USB 1.x/2.0 Mini/Micro pinout

Pin	Name	Wire color	Description
1	VBUS	Red	+5 V
2	D−	White	Data−
3	D+	Green	Data+
4	ID	N/A	Permits detection of which end of a cable is plugged in: • "A" connector (host): connected to the signal ground • "B" connector (device): not connected
5	GND	Black	Signal ground

Colors[edit]

Usual USB color-coding

Color	Description
Black or white	USB 1.x or USB 2.0
Blue	USB 3.0
Yellow, orange or red (USB ports only)	High-current or sleep-and-charge

USB ports and connectors are often color-coded to distinguish their different functions and USB versions. These colors are not part of the USB specification and can vary between manufacturers;^{[citation needed]} for example, USB 3.0 specification mandates appropriate color-coding while it only recommends blue inserts for Standard-A USB 3.0 connectors and plugs.^[67]

Cabling[edit]

A USB twisted pair, where the "Data +" and "Data −" conductors are twisted together in a double helix. The wires are enclosed in a further layer of shielding.

The data cables for USB 1.x and USB 2.x use a twisted pair to reduce noise and crosstalk. USB 3.0 cables contain twice as many wires as USB 2.x to support SuperSpeed data transmission, and are thus larger in diameter.^[68]