USB (Universal Serial Bus- “universal serial bus”) - a serial data transfer interface for medium- and low-speed peripheral devices. A 4-wire cable is used for connection, with two wires used to receive and transmit data, and 2 wires to power the peripheral device. Thanks to the built-in USB power lines allows you to connect peripheral devices without its own power supply.

USB Basics

USB cable consists of 4 copper conductors - 2 power conductors and 2 data conductors in twisted pair, and a grounded braid (screen).USB cables have physically different tips “to the device” and “to the host”. It is possible to implement a USB device without a cable, with a “to-host” tip built into the housing. It is also possible to permanently integrate the cable into the device(for example, USB keyboard, Web camera, USB mouse), although the standard prohibits this for full and high speed devices.

USB bus strictly oriented, i.e. it has the concept of “main device” (host, also known as a USB controller, usually built into the south bridge chip on the motherboard) and “peripheral devices”.

Devices can receive +5 V power from the bus, but may also require an external power supply. A standby mode is also supported for devices and splitters upon command from the bus, removing the main power while maintaining standby power and turning it on upon command from the bus.

USB supportsHot plugging and unplugging of devices. This is possible due to the increase in the length of the grounding contact conductor in relation to the signal ones. When connected USB connector are the first to close grounding contacts, the potentials of the housings of the two devices become equal and further connection of the signal conductors does not lead to overvoltages, even if the devices are powered from different phases of a three-phase power network.

At the logical level, a USB device supports data transfer and reception transactions. Each packet of each transaction contains a number endpoint on the device. When a device is connected, drivers in the OS kernel read a list of endpoints from the device and create control data structures to communicate with each endpoint on the device. The collection of endpoints and data structures in the OS kernel is called pipe.

Endpoints, and therefore channels, belong to one of 4 classes:

• continuous (bulk),
• manager (control),
• isochronous (isoch),
• interrupt.

Low speed devices such as a mouse cannot have isochronous and flow channels.

Control channel designed for exchanging short question-answer packets with the device. Any device has control channel 0, which allows the OS software to read brief information about the device, including manufacturer and model codes used to select a driver, and a list of other endpoints.

Interrupt channel allows you to deliver short packets in both directions, without receiving a response/confirmation, but with a guarantee of delivery time - the packet will be delivered no later than in N milliseconds. For example, used in input devices (keyboards, mice or joysticks).

Isochronous channel allows you to deliver packets without a guarantee of delivery and without replies/confirmations, but with a guaranteed delivery speed of N packets per bus period (1 KHz for low and full speed, 8 KHz for high speed). Used to transmit audio and video information.

Flow channel provides a guarantee of delivery of each packet, supports automatic suspension of data transmission due to device reluctance (buffer overflow or underrun), but does not guarantee delivery speed and delay. Used, for example, in printers and scanners.

Bus time is divided into periods, at the beginning of the period the controller transmits the “beginning of period” packet to the entire bus. Then, during the period, interrupt packets are transmitted, then isochronous ones in the required quantity; for the remaining time in the period, control packets are transmitted, and lastly, stream packets.

Active side of the bus is always the controller, the transfer of a data packet from the device to the controller is implemented as a short question from the controller and a long response from the device containing data. The packet movement schedule for each bus period is created jointly by the controller hardware and driver software; for this, many controllers use Direct Memory Access DMA (Direct Memory Access) - mode of data exchange between devices or between the device and the main memory, without the participation of the Central Processor (CPU). As a result, the transfer speed is increased since data is not sent back and forth to the CPU.

The packet size for an endpoint is a constant built into the device's endpoint table and cannot be changed. It is selected by the device developer from among those supported by the USB standard.

USB Specifications

Features, advantages and disadvantages of USB:

• High transfer speed (full-speed signaling bit rate) - 12 Mb/s;
• The maximum cable length for high transfer speed is 5 m;
• Low-speed signaling bit rate - 1.5 Mb/s;
• The maximum cable length for low communication speed is 3 m;
• Maximum connected devices (including multipliers) - 127;
• It is possible to connect devices with different baud rates;
• There is no need to install additional elements such as terminators;
• Supply voltage for peripheral devices - 5 V;
• The maximum current consumption per device is 500 mA.

USB signals are transmitted over two wires of a shielded 4-wire cable.

USB 1.0 and USB 2.0 connector pinout

Type A		Type B
Fork (on cable)	Socket (on the computer)	Fork (on cable)	Socket (on peripheral device)

Names and functional assignments of USB 1.0 and USB 2.0 pins

Disadvantages of USB 2.0

At least the maximum USB 2.0 data transfer rate is 480 Mbit/s (60 MB/s), in real life it is unrealistic to achieve such speeds (~33.5 MB/s in practice). This is due to the large delays on the USB bus between the request for data transfer and the actual start of the transfer. For example, FireWire, although it has a lower peak throughput of 400 Mbps, which is 80 Mbps (10 MB/s) less than USB 2.0, actually allows for greater data transfer throughput to hard drives and other storage devices. In this regard, various mobile drives have long been limited by the insufficient practical bandwidth of USB 2.0.

The USB connector has been in use since 1997. Then it was installed in computer motherboards. Now it has received widespread implementation: it is used in smartphones and players, printers and a bunch of other devices. More and more advanced versions of USB are coming out. The article will tell you how they differ from each other, as well as the features of their pinout.

Types of USB connectors

Before moving on to the story of USB pinouts by color, you should first understand the types of such an interface. Firstly, they differ in size. Nowadays the standard one is in use, for example, for a computer, and the micro one is used in mobile phones and peripheral devices. Mini is also available, but this type of connector is already becoming obsolete.
USB is also divided into 2 types:

• A - connects to the “mother” socket on the computer or;
• B - connects to the male socket on the peripheral device.

Now let's talk about the types and their differences.

1. v1 - a modified version of version 1.0, the use of which was decided to be discontinued due to numerous errors in the data transfer protocol. It had a low throughput compared to modern representatives.

Main parameters:

• Two modes that differ in the speed with which information is transmitted: 12 and 1.5 Mb/s.
• A cord with a maximum length of three meters is for slow information exchange, and 5 meters for fast information exchange.
• The bus voltage is 5V (nominal), which made it possible to use plugs for charging smartphones, and the permissible load of devices connected to the connector is 0.5 A.

USB pinout by color

Pinouts are indicated by certain colors - these are generally accepted standards that simplify repair tasks. And in general, the color scheme makes it easier to understand which cable is responsible for what.
The first and second versions of the USB interface have identical designations and locations. Generation III has differences related to design and speed features. Read more in the following sections.

USB 2.0 wiring

The table below schematically explains what the color pinout of ports of this generation looks like.

It is worth noting that types A and B have the same circuits. The only difference is that in A the arrangement is linear, while B differs in the arrangement above and below, as in the table:

USB 3.0

In the 3rd branch (this cable belongs to this type) there are 9, sometimes 10 connectors. It all depends on the presence or absence of shielding braid. Naturally, the number of contacts has also increased, but they are placed in a checkerboard pattern. This is necessary for compatibility with older versions.

Alternative connection methods, such as USB connectors, are widely used to connect modern devices.

This name is quite common and is translated from English as “universal serial bus”.

All USB connectors are available in three versions.

Characteristic features of the main three versions of USB connectors

First version of USB connectors (1.1). Its characteristic feature is a very low speed, at which all information is transmitted with a long delay.

The transfer speed is 12 Mbit/s. Its main purpose is to be used for interconnecting devices.

Second version of USB connectors (2.0).

Characterized by a data transfer rate of 480 Mbit/s. This corresponds to a speed of 48 MB/s.

The bulk of all modern technical instruments and devices are adapted to use this particular version. It is the most popular and well-known, and therefore is in demand in the electrical goods market.
True, due to many factors, the real speed of this standard does not exceed 30 - 33 MB/s.

Since the latest releases of hard drives, for example, SSDs, are designed to read information at a much higher speed (almost 4 times), this version of the standard delays the effect of new drive models.

This shows the main drawback of the properties of USB 2.0 connectors. But despite this, certain devices are quite compatible with this version of connectors: mice, keyboards, scanners and printers.

Third version of USB (3.0).

This version is characterized by the speed of information transfer – 5 Gbit/s – which is considered a fairly high figure.

This speed corresponds 500 MB/s

This is much higher than the speed of the latest generation hard drives (150 - 170 MB/s).

USB 3.0 connectors are specially marked blue for recognition.

Interface compatibility

If we consider the issue of compatibility of devices that have the connectors presented above, we can state that the first and second versions of USB connectors can be interchangeable with each other.

A particular device that has a USB version 2 connection but accepts a version 1 connection may display a message indicating its ability to perform faster.

Because this computer model is designed to receive information through the second version, the speed of which is higher than the first.

That is, the full speed potential of this device will not be used.
Modern devices that have connectors of the second version can be connected to the third version of USB, and the use of the third version relative to the second is excluded, except for USB 3.0 type A.

Additional contacts create conditions for increasing the speed of the interface - this is a feature of the latest models of cables and devices that have connectors of the third version of USB.

USB power supply

The power for which connected devices with USB connectors are designed is 2,5 W and also 4,5 W (for the third version).

Based on this, USB connectors of all versions require voltage 5 V. Current up to 0,5 Oh, and for the third version - 0.9 A.

USB 3.0 pins.

Devices such as players, memory cards, phones, flash drives (that is, devices with low power) can be freely connected using such connectors.

And technical means with high power are connected to an external electrical network.

Connector types

The second and third versions of connectors are distinguished by size: Mini USB (small sizes), Micro USB (even smaller sizes); and also by types: A, B.

USB 2.0 type A connector.

A reliable connector whose main characteristic is the ability to withstand more than one connection without losing its integrity.

The cross-section of the connector has a rectangular shape, which creates additional protection when connecting.

Its disadvantage is its large size, and all modern devices are portable, which influenced the development and production of connectors of a similar type, but of a smaller size.

USB 2.0 Type A was introduced in the nineties and is currently still the most used.

A significant number of low-power devices have it: keyboard, mouse, flash drive and others.

USB connector version 2.0 type B.

We mainly find its application in stationary devices of large dimensions. These include scanners, printers, and less commonly ADSL modems.

It is rare, but it still happens that cables of this type are sold separately from the equipment itself, because they are not part of the technical device kit. Therefore, check the complete set of devices.

Connectors of this type are not as popular as type A connectors.

The square and trapezoidal shape is inherent in all type B connectors.

These include both Mini and Micro.

The peculiarity of the cross-section of type “B” connectors is their square shape, which distinguishes it from other types.

Mini USB connectors of the second version, type B.

The name of this type of connector indicates that it has very small dimensions. And this is not surprising, because the modern market increasingly offers miniature goods.

Thanks to the use of personal hard drives, card readers, players and other small devices, USB Mini connectors related to type B have become very popular.

It should be noted that such connectors are unreliable. It becomes loose with frequent use.

But the use of USB Mini Type A connector models is extremely limited.

Micro USB 2.0 type B connectors.

Micro USB connector models are more advanced than Mini USB models.

This type of connector is incredibly small in size.

Unlike the previous mini types presented, these connectors are very reliable with their fastenings and connection fixation.

The Micro USB 2.0 connector type “B” has been recognized in its qualities as uniform for universal use for charging all portable devices.

What will happen over time, when all manufacturers begin to produce equipment adapted specifically to such connectors. It probably won't take long to see it.

But this decision was already made in 2011 by all modern manufacturers, although the Micro USB 2.0 type “B” connector is not yet present on all devices.

USB third version type A connectors.

USB 3.0 connectors have greater speed for information transfer due to additional contacts.

With such changes, feedback compatibility is still maintained. Its use has been established in computers and laptops of the latest generation.

USB connectors third version type B.

The third version of USB type “B” connectors are not suitable for connecting USB connectors of the second version.

It is used in the operation of peripheral devices with medium and large productivity.

Micro USB 3.0.

Modern high-speed external drives, as well as SSD-type drives, are basically all equipped with a connector that is characterized by a high speed of information exchange.

It is increasingly occupying a leading position due to the fact that it has very high-quality connections.

The connector is easy to use due to its compact size. Its predecessor is considered to be a Micro USB connector.

Connector pinoutUSB.

The main differences between Micro and Mini USB connectors

At first glance, these connectors are very similar. Indeed, most of the characteristic features of the basic parameters of these species coincide.

But upon closer inspection, you can notice the following differences:

1. The USB Mini connector is larger than the USB Micro connector.
2. The presence of special-purpose latches on the back side of the USB Micro connectors.

Many users have already become convinced that it is most convenient to have not just one type of connector, but several, because different types of devices have different types of USB connectors.

Unfortunately, device manufacturers have not yet come to a single standard, and most likely will not come for a long time, because each type of USB connector has its own purpose.

The USB type connector is widely used as an interface connector for household devices, and is also actively penetrating into the professional sphere. Provides information exchange between various modern electronic devices, as well as remote power supply of low-power terminal devices.

Interface cables with USB connectors are widely available on sale. In practice, there is a need for a homemade connecting cord of this type, which replaces a failed or simply lost purchased cable, provides the required length, or there is a need for an adapter between USB ports of different types.

Features of USB connectors

In total, three main versions of USB interfaces were standardized. Each new one provided an increase in the speed of information volume and increased functionality. At the same time, taking into account the expansion of application areas, the form factor of the plugs changed.

The ability to connect a cable to a device automatically means that the connected devices are compatible with each other.

USB cable plugs come in full, mini and micro form factors. A type A plug is always included in the central device; a type B plug is intended for servicing the peripheral device. In addition, plugs are divided into type M (from the English male - plug) and F (from the English female - socket).

USB cable wiring by color

PinoutUSB connector differs in that version 2 interface cables use four wires (mini and micro versions - 5 wires), while in version 3 the number of wires is increased to nine.

USB connector wiring made easier by the fact that the wires of a standard cable are assigned specific colors, shown in the table below.

The fifth wire in mini and micro connectors of type B is not used, but in connectors of type A it is shorted to the GND wire.

The screen drain wire (if present) is not assigned a separate number.

A summary of the distribution of wires of USB interfaces version 2 across the pins of various types of plugs is shown in the figure below.

USB cable wiring by color

USB 3.0 pinout

For USB version 3, the pin layout is shown in the figure below.

USB 3.0 cable wiring by color

When making a cable, individual wires and shields are soldered to the corresponding contacts of the plugs.

USB (Universal Serial Bus) - The USB data transfer interface is widespread today, used in almost all devices - phones, PCs, MFPs, tape recorders and other devices - used both for data transfer and for charging phone batteries.

Types of USB connectors.

There are a large number of types of USB connectors. All of them are shown below.

Type A- active, power supply device (computer, host). Type B- passive, connected device (printer, scanner)

USB cable pinout by color.

USB 2.0 pinout.

USB is a serial bus. It uses 4 shielded wires: two for power (+5v & GND) and two for differential data signals (labeled D+ and D-).

USB micro

USB micro has been used since 2011 in phones, MP3 and other devices. Micro is a newer variation of the mini connector. It has the advantage of connecting connectors, the connector is connected tightly to the plug and provides a tight connection.