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USB On-The-Go (OTG) protocol

Short answer

USB On‑The‑Go supplements USB 2.0, letting a device act as both host and peripheral without a PC. A Micro‑AB receptacle and ID pin define the default role; Host Negotiation Protocol swaps roles, and Session Request Protocol wakes a host to save power.

Explain USB-OTG in brief.

USB On-The-Go (OTG) is a supplement to the USB 2.0 standard that lets a portable device act as a host as well as a peripheral, so two devices (for example a camera and a printer, or a phone and a pen drive) can communicate without a PC.

  • A device with OTG has a dual-role function and a Micro-AB receptacle; the ID pin of the plug decides the role: A-device (ID grounded) is the default host and supplies power; B-device is the default peripheral.
  • HNP (Host Negotiation Protocol) allows the two devices to swap host and peripheral roles without changing the cable.
  • SRP (Session Request Protocol) lets a B-device ask the A-device to turn on VBUS to save power.
  • OTG hosts support a limited set of peripherals (targeted peripheral list) and supply a small current (at least 8 mA, typically 100 mA or more).

✓ Answer checked by Claude Sonnet 5.5

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