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The USB On-The-Go logo

USB On-The-Go (USB OTG or just OTG) is a specification first used in late 2001 that allows USB devices, such as tablets or smartphones, to act as a host, allowing other USB devices, such as USB flash drives, digital cameras, mouse or keyboards, to be attached to them. Use of USB OTG allows those devices to switch back and forth between the roles of host and device. A mobile phone may read from removable media as the host device, but present itself as a USB Mass Storage Device when connected to a host computer.

USB OTG introduces the concept of a device performing both master and slave roles – whenever two USB devices are connected and one of them is a USB OTG device, they establish a communication link. The device controlling the link is called the master or host, while the other is called the slave or peripheral.

USB OTG defines two roles for devices: OTG A-device and OTG B-device, specifying which side supplies power to the link, and which initially is the host. The OTG A-device is a power supplier, and an OTG B-device is a power consumer. In the default link configuration, the A-device acts as a USB host with the B-device acting as a USB peripheral. The host and peripheral modes may be exchanged later by using Host Negotiation Protocol (HNP).

The initial role of each device was defined by which mini plug a user inserts into its receptacle.^[1]

USB over Ethernet - USB Network Gate enables work with the remote USB devices over Ethernet (Internet/LAN/WAN) as if they were plugged into your own machine. It helps you share a USB device over network among multiple computers so people from all over the world (or your office) can use it.

Overview[edit]

A USB OTG setup involving a number of devices

Printer drivers in different operating systems Unix and Unix-like. Unix and other Unix-like systems such as Linux and OS X use CUPS (short for Common Unix Printing System), a modular printing system for Unix-like computer operating systems, which allows a computer to act as a print server.A computer running CUPS is a host that can accept print jobs from client computers, process them, and send.
Converters to device-specific format. These drivers convert print data from one format (e.g. PS) to a final device-specific format that the printer hardware can process and create a print. These drivers act as the last stage in delivering a print job to the printer. These drivers are more likely to be embedded in printer firmware.
A USB 3.0 cable or device may be plugged into a USB 2.0 port, but the super speed rate will only work with USB 3.0 cables, devices and ports. USB 3.0 technology will be able to upload and download simultaneously from separate wire lanes of traffic (two wires to transmit, two wires to receive data).
The USB mass storage device class (also known as USB MSC or UMS) is a set of computing communications protocols, specifically a USB Device Class, defined by the USB Implementers Forum that makes a USB device accessible to a host computing device and enables file transfers between the host and the USB device. To a host, the USB device acts as an external hard drive; the protocol set.

Standard USB uses a master/slave architecture; a host acts as the master device for the entire bus, and a USB device acts as a slave. If implementing standard USB, devices must assume one role or the other, with computers generally set up as hosts, while (for example) printers normally function as slaves. In the absence of USB OTG, cell phones often implemented slave functionality to allow easy transfer of data to and from computers. Such phones, as slaves, could not readily be connected to printers as they also implemented the slave role. USB OTG directly addresses this issue.

When a device is plugged into the USB bus, the master device, or host, sets up communications with the device and handles service provisioning (the host's software enables or does the needed when acting as a link slave. The choice between host and peripheral roles is handled entirely by which end of the cable the device is connected to. The device connected to the 'A' end of the cable at start-up, known as the 'A-device', acts as the default host, while the 'B' end acts as the default peripheral, known as the 'B-device'.

After initial startup, setup for the bus operates as it does with the normal USB standard, with the A-device setting up the B-device and managing all communications. However, when the same A-device is plugged into another USB system or a dedicated host becomes available, it can become a slave.

USB OTG does not preclude using a USB hub, but it describes host-peripheral role swapping only for the case of a one-to-one connection where two OTG devices are directly connected. Role swapping does not work through a standard hub, as one device will act as a host and the other as a peripheral until they are disconnected.

Specifications[edit]

USB OTG is a part of a supplement^[2] to the Universal Serial Bus (USB) 2.0 specification originally agreed upon in late 2001 and later revised.^[3] The latest version of the supplement also defines behavior for an Embedded Host which has targeted abilities and the same USB Standard-A port used by PCs.

SuperSpeed OTG devices, Embedded Hosts and peripherals are supported through the USB OTG and Embedded Host Supplement^[4] to the USB 3.0 specification.

Protocols[edit]

The USB OTG and Embedded Host Supplement to the USB 2.0 specification introduced three new communication protocols:

Attach Detection Protocol (ADP)

Allows an OTG device, embedded host or USB device to determine attachment status in the absence of power on the USB bus, enabling both insertion-based behavior and the capability to display attachment status. It does so by periodically measuring the capacitance on the USB port to determine whether there is another device attached, a dangling cable, or no cable. When a large enough change in capacitance is detected to indicate device attachment, an A-device will provide power to the USB bus and look for device connection. At the same time, a B-device will generate SRP (see below) and wait for the USB bus to become powered.

Session Request Protocol (SRP)

Allows both communicating devices to control when the link's power session is active; in standard USB, only the host is capable of doing so. That allows fine control over the power consumption, which is very important for battery-operated devices such as cameras and mobile phones. The OTG or embedded host can leave the USB link unpowered until the peripheral (which can be an OTG or standard USB device) requires power. OTG and embedded hosts typically have little battery power to spare, so leaving the USB link unpowered helps in extending the battery runtime.

Open Usb Device

Host Negotiation Protocol (HNP)

Allows the two devices to exchange their host/peripheral roles, provided both are OTG dual-role devices. By using HNP for reversing host/peripheral roles, the USB OTG device is capable of acquiring control of controllers rather than 'OTG controllers'.

For integrated circuit (IC) designers, an attractive feature of USB OTG is the ability to achieve more USB capabilities with fewer gates.

A 'traditional' approach includes four controllers, resulting in more gates to test and debug:

USB high speed host controller based on EHCI (a register interface)
Full/low speed host controller based on OHCI (another register interface)
USB device controller, supporting both high and full speeds
Fourth controller to switch the OTG root port between host and device controllers

Also, most gadgets must be either a host or a device. OTG hardware design merges all of the controllers into one dual-role controller that is somewhat more complex than an individual device controller.

Targeted peripheral list (TPL)[edit]

A manufacturer's targeted peripheral list (TPL) serves the aim of focusing a host device towards particular products or applications, rather than toward its functioning as a general-purpose host, as is the case for typical PCs. The TPL specifies products supported by the 'targeting' host, defining what it needs to support, including the output power, transfer speeds, supported protocols, and device classes. It applies to all targeted hosts, including both OTG devices acting as a host and embedded hosts.

Plug[edit]

Usb Device Drivers Windows 10

Standard, mini, and micro USB plugs (not to scale). The white areas in the drawings represent hollow spaces. As the plugs are shown here, the USB logo (with optional letter A or B) is on the top of the overmold in all cases. Pin numbering (looking into receptacles) is mirrored from plugs, such that pin 1 on plug connects to pin 1 on the receptacle.

OTG mini plugs[edit]

The original USB OTG standard introduced a plug receptacle called mini-AB that was replaced by micro-AB in later revisions (Revision 1.4 onwards). It can accept either a mini-A plug or a mini-B plug, while mini-A adapters allows connection to standard-A USB cables coming from peripherals. The standard OTG cable has a mini-A plug on one end and a mini-B plug on the other end (it can not have two plugs of the same type).

The device with a mini-A plug inserted becomes an OTG A-device, and the device with a mini-B plug inserted becomes a B-device (see above). The type of plug inserted is detected by the state of the ID pin (the mini-A plug's ID pin is grounded, while the mini-B plug's is floating).

Pure mini-A receptacles also exist, used where a compact host port is needed, but OTG is not supported.

OTG micro plugs[edit]

With the introduction of the USB micro plug, a new plug receptacle called micro-AB was also introduced. It can accept either a micro-A plug or a micro-B plug. Micro-A adapters allow for connection to standard-A plugs, as used on fixed or standard devices. An OTG product must have a single micro-AB receptacle and no other USB receptacles.^[5]^[6]

An OTG cable has a micro-A plug on one end, and a micro-B plug on the other end (it cannot have two plugs of the same type). OTG adds a fifth pin to the standard USB connector, called the ID-pin; the micro-A plug has the ID pin grounded, while the ID in the micro-B plug is floating. A device with a micro-A plug inserted becomes an OTG A-device, and a device with a micro-B plug inserted becomes a B-device. The type of plug inserted is detected by the state of the pin ID.

Three additional ID pin states are defined^[5] at the nominal resistance values of 124 kΩ, 68 kΩ, and 36.5 kΩ, with respect to the ground pin. These permit the device to work with USB Accessory Charger Adapters that allows the OTG device to be attached to both a charger and another device simultaneously.^[7]

These three states are used in the cases of:

A charger and either no device or an A-device that is not asserting V_BUS (not providing power) are attached. The OTG device is allowed to charge and initiate SRP but not connect.^[7]
A charger and an A-device that is asserting V_BUS (is providing power) are attached. The OTG device is allowed to charge and connect but not initiate SRP.^[7]
A charger and a B-device are attached. The OTG device is allowed to charge and enter host mode.^[7]

USB 3.0 introduced a backwards compatible SuperSpeed extension of the micro-AB receptacle and micro-A and micro-B plugs. They contain all pins of the non-Superspeed micro connectors and use the ID pin to identify the A-device and B-device roles, also adding the SuperSpeed pins.

OTG micro cables[edit]

USB OTG adapters, hubs and card readers

Founder Usb Devices Driver Download

When an OTG-enabled device is connected to a PC, it uses its own USB-A or USB Type-C cable (typically ending in micro-B, USB-C or Lightning plugs for modern devices). When an OTG-enabled device is attached to a USB slave device, such as a flash drive, the slave device must either end in the appropriate connection for the device, or the user must supply an appropriate adapter ending in USB-A. The adapter enables any standard USB peripheral to be attached to an OTG device. Attaching two OTG-enabled devices together requires either an adapter in conjunction with the slave device's USB-A cable, or an appropriate dual-sided cable and a software implementation to manage it. This is becoming commonplace with USB Type-C devices.

Smartphone and tablet implementation[edit]

BlackBerry 10.2 implements Host Mode (like in the BlackBerry Z30 handset).^[8] Nokia has implemented USB OTG in many of their Symbian cellphones such as Nokia N8, C6-01, C7, Oro, E6, E7, X7, 603, 700, 701 and 808 Pureview. Some high-end Android phones produced by HTC, and Sony under Xperia series also have it.^[9] Samsung^[10]^[11]Android version 3.1 or newer supports USB OTG, but not on all devices.^[12]^[13]

Host-powered: Sony Ericsson Xperia pro
Needs external USB-power: Motorola Droid 4

Specifications listed on technology web sites (such as GSMArena, PDAdb.net, PhoneScoop, and others) can help determine compatibility. Using GSMArena as an example, one would locate the page for a given device, and examine the verbiage under Specifications → Comms → USB. If 'USB Host' is shown, the device should be capable of supporting OTG-type external USB accessories.^[14]^[15]

In many of the above implementations, the host device has only a micro-B receptacle rather than a micro-AB receptacle. Although non-standard, micro-B to micro-A receptacle adapters are widely available and used in place of the mandated micro-AB receptacle on these devices.^[16]

Backward compatibility[edit]

USB OTG devices are backward-compatible with USB 2.0 (USB 3.0 for SuperSpeed OTG devices) and will behave as standard USB hosts or devices when connected to standard (non-OTG) USB devices. The main exception is that OTG hosts are only required to provide enough power for the products listed on the TPL, which may or may not be enough to connect to a peripheral that is not listed. A powered USB hub may sidestep the issue, if supported, since it will then provide its own power according to either the USB 2.0 or USB 3.0 specifications.

Some incompatibilities in both HNP and SRP were introduced between the 1.3 and 2.0 versions of the OTG supplement, which can lead to interoperability issues when using those protocol versions.

Charger compatibility[edit]

Some devices can use their USB ports to charge built-in batteries, while other devices can detect a dedicated charger and draw more than 500 mA (0.5 A), allowing them to charge more rapidly. OTG devices are allowed to use either option.^[7]

References[edit]

^Koeman, Kosta (22 November 2001). 'Understanding USB On-The-Go'. edn.com. EDN. Retrieved 20 June 2017.
^'On-The-Go and Embedded Host Supplement to the USB 2.0 Specification, Revision 2.0 plus ECN and errata'. USB.org. 14 July 2011. Archived from the original on 5 May 2012. Retrieved 18 July 2005.
^Heise, Heinz. 'USB-On-the-Go-Specification Settled'. Heise.de.^{[dead link]}
^'On-The-Go and Embedded Host Supplement to the USB Revision 3.0 Specification, Revision 1.1'. USB.org. May 10, 2012.
^ ^a^b'Universal Serial Bus Revision 2.0 specification'. On-The-Go and Embedded Host Supplement to the USB Revision 2.0 Specification, Revision 2.0 version 1.1a. USB Implementers Forum, Inc. 27 July 2012. Retrieved 26 June 2017.^{[permanent dead link]}
^'Universal Serial Bus Revision 2.0 specification'. Universal Serial Bus Micro-USB Cables and Connectors Specification, Revision 1.01. USB Implementers Forum, Inc. 4 April 2007. Retrieved 26 June 2017.^{[permanent dead link]}
^ ^a^b^c^d^e'Battery Charging Specification'. USB Implementers Forum, Inc. 15 April 2009. Archived from the original on 4 March 2016. Retrieved 23 September 2009.
^KB34983-Support for USB Embedded Host mode on BlackBerry 10 OS version 10.2
^'USB On the Go - HTC Blog'. blog.htc.com.
^'Samsung Galaxy S II Able To Use Standard USB OTG Cable For USB On-The-Go Access - TalkAndroid.com'. www.talkandroid.com.
^'Xperia S USB OTG demonstrated [Video] - Xperia Blog'. www.xperiablog.net.
^'Android Issue 738: I hope Android will implement and support the USB host feature'. Google.com. 30 May 2008. Retrieved 30 May 2013.
^'USB Host – Android Developers'. developer.android.com. 30 May 2013. Retrieved 30 May 2013.
^http://www.gsmarena.com/ GSMArena
^http://pdadb.net PDAdb.net
^'Are Micro A USB plugs actually ever used?'. Electrical Engineering Stack Exchange. Retrieved 13 August 2020.

External links[edit]

'USB OTG Flash Drives'. Kingston.
Broida, Rick (5 February 2014). 'How to tell if your Android phone or tablet supports USB On-The-Go'. CNet. Refers to two apps, to verify OTG compatibility, and to overcome (root) and enable OTG

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