What is USB OTG

What is USB OTG? All You Need to Know About USB On-The-Go

What is USB OTG? All You Need to Know About USB On-The-Go - Table of contents:

USB OTG is the abbreviation of USB On-The-Go. It is a technology developed in recent years.

It was announced by USB Implementers Forum on December 18, 2001.

It is mainly used in the connection between various devices or mobile devices for data exchange. Especially PAD, mobile phones, and consumer equipment.

What is USB OTG


USB OTG is a supplementary standard for the USB 2.0 specification. It enables USB devices, such as a player or a mobile phone, to change from a USB peripheral to a USB host to communicate with other USB devices.

Under normal circumstances, these OTG-enabled USB devices and USB hosts (such as desktops or laptops) are still used as USB peripheral devices.

OTG-enabled devices, such as a USB printer, can directly access a U disk to print files in the device without connecting to a computer, or an poe android tablet can directly access a USB storage disk, keyboard, or mouse to expand external hardware functions.

USB Structure

The standard USB uses a master-slave architecture, with the USB host (the computer) being the “master” and the USB peripheral being the “slave”. Only the USB server can schedule the settings and data transfer of this link. USB peripherals cannot initiate data transmission by themselves and can only respond to instructions from the server.

What is USB OTG

USB OTG Change this situation, accessories no longer have to be simple peripheral devices, they can sometimes become the host side. For example, when the USB printer is connected to the computer the outer periphery of the computer is controlled by the computer, and the other USB storage device serves as the control host computer to read the storage device when the computer is connected to the computer, and is connected to the USB storage device or USB input device as the storage device or receives the input.

However, few manufacturers support this, mainly digital partners support this feature, and mobile phones and tablets allow and use Windows Mobile or Android support in hardware. Many players are starting to support this feature, but most only support reading on the main side.

USB OTG has the following features:

  • The interface is more compact, effectively reducing the volume of electronic products.
  • It can act as both a HOST and a Device, that is, DRD (Dual-role-devices).
  • The OTG device can still be connected to the PC as a common peripheral, such as POD (Peripheral-Only-Device).
  • Lower power consumption to extend the standby time of battery-powered USB devices.

There are three new communication protocols for USB OTG and embedded hosts of the USB 2.0 specification:

Additional Detection Protocol (ADP)

Allows OTG devices, embedded hosts, or USB devices to determine connection status when the USB bus is not powered, while activating plug-in-based behavior and functionality to display the connection status. It works by periodically measuring the capacitance on the USB port to determine if another device is connected, a dangling cable or no cable. When a large enough capacitance change is detected to indicate a device connection, the A-device will apply power to the USB bus and look for a device connection. Meanwhile, the B-device will generate an SRP and wait for the USB bus to power up.

Session Request Protocol (SRP)

A power session that allows a communicating device to control the link when it is active; in standard USB, only the host is able to do so. This allows precise control of power consumption, which is important for battery-operated devices such as cameras and cell phones. An OTG or embedded host can power down the USB link until the peripheral (which can be an OTG or standard USB device) requires power. OTG and embedded hosts typically have very little battery power available, so powering down the USB link will help extend battery run time.

Host Negotiation Protocol (HNP)

Allows the two devices to swap their host/peripheral roles, provided both devices are OTG dual-role devices. By using HNP to reverse the host/peripheral role, a USB OTG device can gain control over the scheduling of data transfers. Therefore, any OTG device can initiate data transfer through the USB OTG bus. The latest version of the supplement also introduces HNP polling, where a host device periodically polls a peripheral during an active session to determine if it wishes to become the host. The main purpose of the HNP is to accommodate users with A and B devices connected (see below) going in the wrong direction for the task they want to perform.

What is USB OTG

For example, a printer connects as an A-device (host), but cannot act as a host to a particular camera because it doesn’t understand what the camera says about the print job. When the camera knows how to talk to the printer, the printer will switch to the slave role using the HNP and the camera becomes the master, so photos stored in the camera can be printed without reconnecting the cable. The new OTG protocols cannot pass through standard USB hubs because they are based on electrical signals passing over dedicated lines.

The USB OTG and Embedded Host Supplement to the USB 3.0 Specification introduces an additional protocol, the Role Swap Protocol (RSP). The same purpose as HNP (that is, role exchange) is achieved by extending the standard mechanism provided by the USB 3.0 specification.

Following the USB OTG and Embedded Host supplements to the USB 2.0 specification, there is also a need to follow the USB 2.0 supplement to maintain backward compatibility. OTG devices with super-speed peripheral functions (SS-OTG) need to support RSP. SuperSpeed Peripheral Capable OTG devices (SSPC-OTG) do not need to support RSP because they can only operate as SuperSpeed Peripheral Capable; they do not have SuperSpeed Peripheral Capable hosts, so can only operate at USB 2.0 data rates Next use HNP for role swapping.

How can OTG be used?

1. Read and write mobile storage devices

For example, if you take pictures with a camera outdoors and want to post them or send them to Moments if you have an OTG cable and a card reader, you can easily import the photos from the camera’s memory card to your phone. In the same way, a U disk and mobile hard disk can also be used in this way.

What is USB OTG

2. Connect peripherals

Connecting the mouse to the mobile phone through OTG is not very useful, to be honest. After all, the touch screen is still convenient for fingers. However, if the screen of your mobile phone is broken and the touch function fails, an external mouse can help you complete basic operations and export important data. In addition, the role of connecting to the keyboard is self-evident. The efficiency of typing has risen sharply, and a small OTG cable can save the money of purchasing another Bluetooth keyboard.

What is USB OTG

3. Reverse charging

After plugging in the OTG cable to USB , connect another mobile phone with a data cable to charge it.

What is USB OTG

Unmarked pictures come from Internet, and source:

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USB OTG Is short for USB On-The-Go, a technology developed in recent years. It was announced by USB Implementers Forum on December 18th, 2001, and is mainly used in the connection of different devices or mobile devices for data exchange, especially PAD, mobile phones, and consumer devices.
There are three. Additional Detection Protocol (ADP), Session Request Protocol (SRP), and Host Negotiation Protocol (HNP).