--- title: "USB 1.1 vs 2.0 and device identification" subject: "Instrumentation II" chapter: 3 key: "semester_5/instrumentation_ii:usb11-vs-usb20-identify" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/usb11-vs-usb20-identify site: BCT Engineering --- # USB 1.1 vs 2.0 and device identification Instrumentation II · Chapter 3: Serial Interfacing With Microprocessor Based System - Asked in: 2068 Chaitra, 6 marks - Video: [USB Protocol Explained: Basics, Versions, Connectors, Working, Signals, and Objectives](https://www.youtube.com/watch?v=6knlPjpa_DE) — Engineering Funda - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/usb11-vs-usb20-identify - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-3 ## Question Differentiate between USB 1.1 and USB 2.0. State briefly how USB 2.0 identifies itself with the interfacing unit and establishes communication protocol. Draw the necessary diagrams. ## Short answer USB 1.1 supports low (1.5) and full (12 Mbps) speeds, 1 ms frames, max 64-byte bulk packets. USB 2.0 adds high speed (480 Mbps), 125 µs microframes, 512-byte bulk packets. For identification, after reset a high-speed device performs a chirp handshake: it sends a chirp K; if the host answers with K-J pairs, the device switches to high speed, then enumeration reads descriptors. ## Answer #### Difference between USB 1.1 and USB 2.0 | Point | USB 1.1 | USB 2.0 | |---|---|---| | Speeds | Low 1.5 Mbps, full 12 Mbps | Low 1.5, full 12, high 480 Mbps | | Signalling | 3.3 V, NRZI | Same, plus high speed with 400 mV signalling and 45 ohm terminations | | Frame | 1 ms frame | 125 us microframes (high speed) | | Max. packet (bulk) | 64 bytes | 512 bytes | | Hubs | Basic | High-speed hubs with transaction translator | | New features | - | PING, split transactions, OTG | | Compatibility | - | Backward compatible with 1.1 | #### How a USB 2.0 device identifies itself and sets up communication 1. **Attachment and speed detection:** on connection the device pulls D+ high through a 1.5 kohm resistor. The host (with 15 kohm pull-downs) senses the J state: it is a full-speed device (low speed: D- pulled up). 2. **Reset:** the host drives SE0 for at least 10 ms. A high-speed capable device then performs the **chirp handshake**: it sends a chirp K; a high-speed host answers with alternating chirp K-J pairs; if the device sees three K-J pairs it removes its D+ pull-up, enables 45 ohm terminations and switches to high speed. Otherwise it stays at full speed. ```text Device Host | --- D+ pull-up --------->| full speed device detected |<---- Reset (SE0) --------| | --- chirp K ------------>| |<-- chirp K J K J K J ----| | (remove pull-up, HS mode)| ``` 3. **Enumeration:** the host sends GET_DESCRIPTOR (first 8 bytes of the device descriptor, default address 0), SET_ADDRESS (new address), full GET_DESCRIPTOR requests (device, configuration, interface, endpoints, strings) and then SET_CONFIGURATION. The descriptor gives USB version (0200H), class, VID/PID and maximum packet size, identifying the device and its protocol. After that data transfers use the assigned address and endpoints. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What speed does USB 2.0 add over USB 1.1? A. SuperSpeed 5 Gbps B. High speed 480 Mbps C. Full speed 12 Mbps D. Low speed 1.5 Mbps Answer: B. USB 1.1 has low and full speed; USB 2.0 adds 480 Mbps high speed. (Key point: Speed difference) 2. How does the host detect a full-speed device? A. K state B. 1.5 kohm pull-up on D+ gives J state C. SE1 D. Pull-up on D- Answer: B. A pull-up on D+ makes the host see J; a D- pull-up indicates low speed. (Key point: Speed detection) 3. How long does the host drive SE0 for reset? A. 1 ms B. 2.5 us C. 100 ms D. At least 10 ms Answer: D. Reset is SE0 for at least 10 ms. (Key point: Reset) 4. What happens in the chirp handshake? A. Device sends chirp K, host replies with K-J pairs, device removes pull-up and goes high speed B. Host sends SE1 C. Device sends SYNC only D. Host removes its pull-down Answer: A. After seeing three K-J pairs the device removes the pull-up and enables 45 ohm terminations. (Key point: Chirp) ## Related in Instrumentation II - [USB enumeration; device vs host interface chips](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ausb-enumeration) — Instrumentation II, chapter 3 - [USB interface chips: device vs host](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ausb-interface-chips) — Instrumentation II, chapter 3 - [USB host, hub, device and packets](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ausb-host-hub-device-packets) — Instrumentation II, chapter 3 - [PC interfacing techniques for I/O device](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Apc-interfacing-techniques) — Instrumentation II, chapter 2, asked 2× - [USB On-The-Go (OTG) protocol](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ausb-otg) — Instrumentation II, chapter 3, asked 3× - [USB 1.1 vs USB 2.0](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ausb11-vs-usb20) — Instrumentation II, chapter 3, asked 3× ## Related in other subjects - [Communication protocol and its need](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Acommunication-protocol-need) — Telecommunications, chapter 8, asked 3× - [Communication protocol and OSI architecture](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aprotocol-osi-architecture) — Telecommunications, chapter 8 - [Power vs refrigeration cycle; Rankine components and diagrams](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Apower-vs-refrigeration-cycle-rankine-components) — Fundamental of Thermodynamics & Heat Transfer, chapter 6 - [Routed vs routing protocol](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Arouted-vs-routing-protocol) — Computer Networks and Security, chapter 4