USB pinout

4 pin USB A or USB B plug connector layout
4 pin USB A or USB B plug connector at the peripherals


4 pin USB A / USB B / mini-USB jack connector layout
4 pin USB A / USB B / mini-USB jack connector

USB (Universal Serial Bus) designed to connect
peripherals such as mice, keyboards, scanners, digital cameras,
printers, hard disks, and networking components to PC. It has become the
standard connection method for scanners, digital cameras and for some
printers. Complete pinout.

Universal Serial Bus (USB) is a specification to
establish communication between devices and a host controller (usually
personal computers). An USB system consists of a host controller and
multiple devices connected  using special hub devices. Hubs may be
cascaded, up to 5 levels.  USB can connect computer peripherals such as
mice, keyboards, digital cameras, PDA, mobile phones, printers, personal media players, flash drives, GPS, Network Adapters, and external hard drives. For many of those devices, USB has become the standard connection method. 

USB interface aimed to remove the need for adding expansion cards into the computer’s PCI or PCI-Express
bus, and improve plug-and-play capabilities by allowing devices to be
hot swapped or added to the system without rebooting the computer.
 

The USB Pinout:

Pin Name Cable color Description
1 VCC Red +5 VDC
2 D- White Data -
3 D+ Green Data +
4 GND Black Ground

Pin x of mini-USB connector
may be not connected, connected to GND or used as attachment
identification at some portable devices. This pin is numbered x here due
to historical reasons. 

USB connectors

There are several types of USB connectors. The original USB
specification detailed Standard-A and Standard-B plugs and receptacles.
Nowdays there are 7 USB connectors known: Standard-A, Standard-B, Mini-A, Mini-B (shown on left), Micro-A, Micro-AB, Micro-B
 

USB pinout signals

USB is a serial bus. It uses 4 shielded wires: two for power (+5v &
GND) and two for differential data signals (labelled as D+ and D- in
pinout). NRZI (Non Return to Zero Invert) encoding scheme used to send
data with a sync field to synchronise the host and receiver clocks. In USB data cable
Data+ and Data- signals are transmitted on a twisted pair. No
termination needed. Half-duplex differential signaling helps to combat
the effects of electromagnetic noise on longer lines. Contrary to
popular belief, D+ and D- operate together; they are not separate
simplex connections. USB 2.0 provides for a maximum cable length of 5
meters for devices running at Hi Speed.

USB transfer modes

Univeral serial bus supports Control, Interrupt, Bulk and Isochronous transfer modes.

USB interfaces: USB 1.0, USB 2.0, USB 3.0.

There are three USB versions known nowdays:

USB 1.0 

  • released in 1996.
  • Specifies data rates of 1.5 Mbit/s (Low-Bandwidth, is mostly used for
    Human Input Devices (HID) such as keyboards, mouses, joysticks and often
    the buttons on higher speed devices such as printers or scanners) and
    12 Mbit/s (Full-Bandwidth).
  • nowadays is still used used by some devices that don’t need faster data transfer rates.

USB 2.0

  • released in 2000
  • in addition to USB 1.0 adds signaling rate of 480 Mbit/s (Hi-Speed)
  • compatible with USB 1.0, but some hardware designed for USB 2.0 may not work with USB 1.0 host controllers.

USB 3.0

  • released in 2008
  • added transmission rates up to 5 Gbit/s (SuperSpeed)

USB 1.0 and USB 2.0 shares same pinout, USB 3.0 pinout features new connectors.

A USB device must indicate its speed by pulling either the D+ or D-
line high to 3.3 volts. These pull up resistors at the device end will
also be used by the host or hub to detect the presence of a device
connected to its port. Without a pull up resistor, USB assumes there is
nothing connected to the bus. 

In order to help user to identify maximum speed of device, a USB device
often specifies its speed on its cover with one of the USB special
marketing logos.

When the new device first plugs in, the host enumerates it and loads
the device driver necessary to run it. The loading of the appropriate
driver is done using a PID/VID (Product ID/Vendor ID) combination
supplied by attached hardware. The USB host controllers has their own
specifications: UHCI (Universal Host Controller Interface), OHCI (Open
Host Controller Interface) with USB 1.1, EHCI (Enhanced Host Controller
Interface) is used with USB 2.0.

USB powered devices

The USB connector provides a single 5 volt wire from which connected
USB devices may power themselves. A given segment of the bus is
specified to deliver up to 500 mA. This is often enough to power several
devices, although this budget must be shared among all devices
downstream of an unpowered hub. A bus-powered device may use as much of
that power as allowed by the port it is plugged into.

Bus-powered hubs can continue to distribute the bus provided power to
connected devices but the USB specification only allows for a single
level of bus-powered devices from a bus-powered hub. This disallows
connection of a bus-powered hub to another bus-powered hub. Many hubs
include external power supplies which will power devices connected
through them without taking power from the bus. Devices that need more
than 500 mA or higher than 5 volts must provide their own power.

When USB devices (including hubs) are first connected they are
interrogated by the host controller, which enquires of each their
maximum power requirements. However, seems that any load connected to
USB port may be treated by operating system as device. The host
operating system typically keeps track of the power requirements of the
USB network and may warn the computer’s operator when a given segment
requires more power than is available and may shut down devices in order
to keep power consumption within the available resource.

USB power usage:

Bus-powered hubs: Draw Max 100 mA at power up and 500 mA normally.
Self-powered hubs: Draw Max 100 mA, must supply 500 mA to each port.
Low power, bus-powered functions: Draw Max 100 mA.
High power, bus-powered functions: Self-powered hubs: Draw Max 100 mA, must supply 500 mA to each port.
Self-powered functions: Draw Max 100 mA.
Suspended device: Max 0.5 mA

Dedicated charger mode:

A simple USB charger should short the 2 data lines together. The device
will then not attempt to transmit or receive data, but can draw up to
1.8A, if the supply can provide it.

USB voltage:

Supplied voltage by a host or a powered hub ports is between 4.75 V and
5.25 V. Maximum voltage drop for bus-powered hubs is 0.35 V from its
host or hub to the hubs output port. All hubs and functions must be able
to send configuration data at 4.4 V, but only low-power functions need
to be working at this voltage. Normal operational voltage for functions
is minimum 4.75 V.

USB cable shielding:

Shield should only be connected to Ground at the host. No device should connect Shield to Ground.

USB cable wires:

Shielded:
Data: 28 AWG twisted
Power: 28 AWG – 20 AWG non-twisted

Non-shielded:
Data: 28 AWG non-twisted
Power: 28 AWG – 20 AWG non-twisted

Power Gauge Max length
28 0.81 m
26 1.31 m
24 2.08 m
22 3.33 m
20 5.00 m

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