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USB On-The-Go
USB On-The-Go (USB OTG) is a specification that allows certain USB devices, such as tablets or smartphones, to function either as a host or a peripheral. This enables them to connect directly to other USB devices, such as flash drives, digital cameras, mice or keyboards. USB OTG was first introduced in late 2001.
Unlike standard USB connections, which involve a fixed host (such as a computer) and a peripheral (such as a keyboard), USB OTG allows a device to switch between these roles. For example, a smartphone can act as a host when reading files from a flash drive, but function as a peripheral when connected to a computer.
USB OTG defines two device roles: the A-device, which supplies power and initially acts as the host, and the B-device, which consumes power and begins as the peripheral. These roles can be reversed using the Host Negotiation Protocol (HNP). The initial role is determined by the wiring of a specific pin, known as the ID pin, in the USB connector. The A/B naming convention reflects earlier USB connector types: Type-A connectors were used with host devices, while Type-B connectors were used with peripherals.
In September 2019 USB Implementers Forum has stopped certifying new USB OTG products because of Introduction of USB-C standard.
Standard USB uses a host/device architecture; a host acts as the Host device for the entire bus, and a USB device acts as a Peripheral. 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 a Peripheral. In the absence of USB OTG, cell phones often implemented Peripheral functionality to allow easy transfer of data to and from computers. Such phones could not readily be connected to printers as they also implemented the peripheral role. USB OTG directly addresses this issue.
When a device is plugged into the USB bus, the host device sets up communications with the device and handles service provisioning (the host's software enables or does the needed data-handling such as file managing or other desired kind of data communication or function). That allows the devices to be greatly simplified compared to the host; for example, a mouse contains very little logic and relies on the host to do almost all of the work. The host controls all data transfers over the bus, with the devices capable only of signalling (when polled) that they require attention. To transfer data between two devices, for example from a phone to a printer, the host first reads the data from one device, then writes it to the other.[citation needed]
While the host-device arrangement works for some devices, many devices can act either as host or as device depending on what else shares the bus. For instance, a computer printer is normally a device, but when a USB flash drive containing images is plugged into the printer's USB port with no computer present (or at least turned off), it would be useful for the printer to take on the role of host, allowing it to communicate with the flash drive directly and to print images from it.[citation needed]
USB OTG recognizes that a device can perform both Host and Peripheral roles, and so subtly changes the terminology. With OTG, a device can be either a host when acting as a link host, or a link peripheral. 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".[citation needed]
Hub AI
USB On-The-Go AI simulator
(@USB On-The-Go_simulator)
USB On-The-Go
USB On-The-Go (USB OTG) is a specification that allows certain USB devices, such as tablets or smartphones, to function either as a host or a peripheral. This enables them to connect directly to other USB devices, such as flash drives, digital cameras, mice or keyboards. USB OTG was first introduced in late 2001.
Unlike standard USB connections, which involve a fixed host (such as a computer) and a peripheral (such as a keyboard), USB OTG allows a device to switch between these roles. For example, a smartphone can act as a host when reading files from a flash drive, but function as a peripheral when connected to a computer.
USB OTG defines two device roles: the A-device, which supplies power and initially acts as the host, and the B-device, which consumes power and begins as the peripheral. These roles can be reversed using the Host Negotiation Protocol (HNP). The initial role is determined by the wiring of a specific pin, known as the ID pin, in the USB connector. The A/B naming convention reflects earlier USB connector types: Type-A connectors were used with host devices, while Type-B connectors were used with peripherals.
In September 2019 USB Implementers Forum has stopped certifying new USB OTG products because of Introduction of USB-C standard.
Standard USB uses a host/device architecture; a host acts as the Host device for the entire bus, and a USB device acts as a Peripheral. 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 a Peripheral. In the absence of USB OTG, cell phones often implemented Peripheral functionality to allow easy transfer of data to and from computers. Such phones could not readily be connected to printers as they also implemented the peripheral role. USB OTG directly addresses this issue.
When a device is plugged into the USB bus, the host device sets up communications with the device and handles service provisioning (the host's software enables or does the needed data-handling such as file managing or other desired kind of data communication or function). That allows the devices to be greatly simplified compared to the host; for example, a mouse contains very little logic and relies on the host to do almost all of the work. The host controls all data transfers over the bus, with the devices capable only of signalling (when polled) that they require attention. To transfer data between two devices, for example from a phone to a printer, the host first reads the data from one device, then writes it to the other.[citation needed]
While the host-device arrangement works for some devices, many devices can act either as host or as device depending on what else shares the bus. For instance, a computer printer is normally a device, but when a USB flash drive containing images is plugged into the printer's USB port with no computer present (or at least turned off), it would be useful for the printer to take on the role of host, allowing it to communicate with the flash drive directly and to print images from it.[citation needed]
USB OTG recognizes that a device can perform both Host and Peripheral roles, and so subtly changes the terminology. With OTG, a device can be either a host when acting as a link host, or a link peripheral. 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".[citation needed]