By definition USB On-The-Go, often abbreviated USB OTG or just OTG, is a specification that allows USB devices such as digital audio players or mobile phones to act as a host, allowing other USB devices like a USB flash drive, mouse, or keyboard to be attached to them.On-the-Go 3.0 is an upgrade to On-the-Go 2.0 and is backwards compatible with past versions. The Embedded Host supplement adds details on how smart appliances like tablets, phones and even cameras will be able to use a single USB 3.0 IP port as either a host or peripheral.
Specifications:
USB OTG is a part of a supplement to the Universal Serial Bus (USB) 2.0 specification originally agreed upon in late 2001 and later revised. The latest version of this 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 On-The-Go and Embedded Host Supplement to the USB 3.0 specification.
Architecture:
USB On-The-Go introduces the concept that a device can perform both the master and slave roles, and so subtly changes the terminology. With SS OTG, a device can be either a host when acting as the link master, or a peripheral when acting as the link slave. The choice of whether to be host or peripheral is handled entirely by which end of the cable the device is plugged into. 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 that same A-device is plugged into another USB system, or a dedicated host becomes available, it may become a slave.
USB On-The-Go 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 the host and the other as the peripheral until they are disconnected.
There are two categories of Targeted Hosts:
1. Embedded Hosts: An Embedded Host (EH) product provides Targeted Host functionality over one or more Standard-A or Micro-AB receptacles. Embedded Host products may also offer USB peripheral capability, delivered separately via one or more Type-B receptacles.
2. On-The-Go: An SS OTG product is a portable device that uses a single Micro-AB receptacle (and no other USB receptacles) to operate at times as a USB Targeted Host and at times as a USB peripheral. OTG devices shall always operate as a standard peripheral when connected to a standard USB host. OTG devices can also be attached to each other. This specification enables the underlying driver components to optionally swap between the role of either USB host or USB peripheral, without needing to physically turn the cable around.
[OTG&EH2.0] applies to all Universal Serial Bus products. This supplement covers products which have a SuperSpeed capability (as defined in the [USB3.0] specification) in addition to having capabilities defined in [OTG&EH2.0]. The following additional configurations are covered by this supplement:
1. SuperSpeed Embedded Host or SS-EH: An Embedded Host which can operate at SuperSpeed through its one or more Standard-A or Micro-AB receptacles in addition to EH capability defined in [OTG&EH2.0] for example support for SRP and ADP.
2. SuperSpeed Peripheral Only or SS-PO: A peripheral-only B-device which can operate at SuperSpeed in addition to having peripheral-only B-device capabilities as described in [OTG&EH2.0].
3. SuperSpeed Peripheral Capable OTG Device or SSPC-OTG: An OTG device compliant with [OTG&EH2.0] which can also operate as a SuperSpeed peripheral. Products with this configuration are not able to operate as a SuperSpeed host. When operating as a peripheral, they can operate at either SuperSpeed or [OTG&EH2.0] speeds. However they may only be able to swap roles when operating at
[OTG&EH2.0] speeds.
4. SuperSpeed OTG Device or SS-OTG: An OTG Device compliant with [OTG&EH2.0] which can also operate as a SuperSpeed Host or a SuperSpeed Peripheral. Products with this configuration may be able to dynamically swap host/peripheral roles while operating at SuperSpeed using the mechanisms defined in this supplement. Devices which conform to [OTG&EH2.0] are referred to as [USB2.0] devices in this supplement: USB2.0
EH, USB2.0 OTG and USB2.0 PO.
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