What is USB ON-THE-GO (OTG) and why must you have it?

All about USB OTG

Hi reader, today we are talking about the USB On-The-Go, often abbreviated as USB OTG or just OTG. It was first used in late 2001 but less people have knowledge about it and how much it is of importance and or beneficial to their everyday life. I first experienced the USB OTG back in 2009 though I just had less than an hour with it, I swore there and then that I must have one of those.

What is USB OTG?

It is a USB device or a USB cable that when connected to a digital audio player or a mobile phone it will allow the USB device to act as a host. USB devices like USB flash drives, digital cameras, mice or keyboards can be attached to them. USB OTG allows those devices to switch back and forth between roles of host and client (communication link). For instance, 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.

What am I saying? Virtually, every portable device now uses USB for PC connectivity. As these products increase in popularity, there is a growing need for them to communicate both with USB peripherals and directly with each other when a PC is not available. There is also an increase in the number of other, non-PC hosts (Embedded Hosts) which support USB in order to connect to USB peripherals. Now the USB On-The-Go comes in and 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 On-The-Go 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.

"How would you feel if you had a separate storage space for your smartphone and you can access it whenever and wherever? or can type messages on your tablet using your USB PC keyboard..."

#TECH101KE Call it your own "cloud connection" with the USB OTG. Learn more https://t.co/zAJMoo04FP pic.twitter.com/XW4KHG6U1t
— JTechpreneur™ (@JTechpreneur) July 29, 2016

How it works

Standard USB uses a master/slave architecture; a host acts as master device for the entire bus, and a USB device acts as slave. Devices are designed from the outset to assume one role or the other – computers are generally set up to be hosts, while, for example, printers are normally slaves.

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 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. While the master/slave arrangement works for some devices, there are many devices capable of acting as either master or slave depending on what else shares the bus. For instance, a computer printer is normally a slave 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 print images from it.
USB On-The-Go recognizes that a device can perform both master and slave roles, and so subtly changes the terminology. With OTG, a device can be either a host when acting as a link master, or a "peripheral" when acting as a link slave

The USB On-The-Go and Embedded Host Supplements addresses these scenarios by allowing portable devices and non-PC hosts to have the following enhancements:

Targeted host capability to communicate with selected other USB peripherals
Support for direct connections between OTG devices
Power saving features to preserve battery life

OTG Communication Protocols

The USB On-The-Go 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 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.

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 data-transfer scheduling. Thus, any OTG device is capable of initiating data-transfer over USB OTG bus. The latest version of the supplement also introduced HNP polling, in which the host device periodically polls the peripheral during an active session to determine whether it wishes to become a host.

Want to make your own? Do this...

Like the article? don't forget to share it on your different social media platforms and also you can Subscribe to our newsletters by typing your email address and submit it below. For more queries and comments, email us at jtechpreneur@gmail.com or submit your comments below.