--- title: "Arbitration methods and I2C significance" subject: "Embedded System" chapter: 5 key: "semester_6/embedded_system:arbitration-types-i2c" source: https://www.bctengineer.com/q/semester_6/embedded_system/arbitration-types-i2c site: BCT Engineering --- # Arbitration methods and I2C significance Embedded System · Chapter 5: Interfacing - Asked in: 2070 Bhadra, 8 marks - Video: [I2C Arbitration | Prodigy Technovations](https://www.youtube.com/watch?v=HNkUwyACuL0) — Prodigy Technovations - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/embedded_system/arbitration-types-i2c - Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-5 ## Question Explain different types of arbitration methods used in peripheral devices to gain control of system bus. Describe the significance of I²C serial communication protocol. ## Short answer Arbitration methods include priority (individual Req/Ack, fixed/rotating), daisy-chain (chained Grant, position priority), and network-oriented (I2C's wired-AND, CSMA/CD). I2C is a two-wire serial protocol (SDA/SCL) supporting multiple masters and slaves with only two wires, built-in arbitration, acknowledgment, 7/10-bit addressing, widely used for low-speed peripherals. ## Answer #### Arbitration methods for gaining control of the system bus Arbitration decides which of several requesting devices becomes bus master. 1. **Priority arbitration:** an arbiter with a Req/Ack line pair per device grants the bus to the highest-priority request. Priority may be fixed or rotating (round robin). 2. **Daisy-chain arbitration:** devices share one Req line; the Grant is passed through the devices in series. The first device in the chain that has requested keeps the grant, so priority depends on position. Simple, but unfair and fault-sensitive. 3. **Network-oriented (distributed) arbitration:** there is no central arbiter. Each device senses the bus and sends when it is idle; collisions are detected and resolved, e.g. CSMA/CD in Ethernet, or bitwise arbitration by identifier priority in CAN (the lower ID wins), or the wired-AND SDA/SCL arbitration in I2C. 4. **Polling / centralised arbiter variants:** the arbiter polls devices in turn (round-robin). #### Significance of the I2C protocol **I2C (Inter-Integrated Circuit)** is a two-wire synchronous serial bus (SDA data and SCL clock) developed by Philips for connecting low-speed peripherals to a processor. - Only **two wires** for many devices, saving pins and board space. - **Multi-master and multi-slave** capability, with 7-bit (or 10-bit) addresses to identify slaves. - Built-in **acknowledge** bit after each byte gives reliable transfer. - Built-in arbitration: if two masters transmit together, the one sending a 0 while the other sends 1 wins (wired-AND), without losing data. - Speeds: 100 kbps standard, 400 kbps fast, 3.4 Mbps high-speed. - Used for EEPROMs, RTC, sensors, ADC/DAC, LCD drivers in embedded systems. Limits: slow compared with SPI and short distance. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In CAN network-oriented arbitration, which message wins? A. The longest message B. The one with the lower identifier C. The one sent first on the cable D. The one with the higher identifier Answer: B. Bitwise arbitration by identifier priority lets the lower ID win. (Key point: CAN bitwise arbitration) 2. How many wires does I2C use and what are they? A. One: data only B. Three: data, clock, select C. Four: MOSI, MISO, SCK, SS D. Two: SDA data and SCL clock Answer: D. I2C is a two-wire synchronous bus, saving pins and board space. (Key point: I2C bus lines) 3. If two I2C masters transmit simultaneously, which one wins and why? A. The one sending 0 while the other sends 1, due to wired-AND, without losing data B. The master with the lower clock speed C. The one sending 1 D. Both stop and restart Answer: A. On a wired-AND bus, 0 overrides 1, so the master sending 0 wins and continues without data loss. (Key point: I2C arbitration) 4. Which is a significance of I2C? A. Speeds above 1 Gbps B. Multi-master/multi-slave with 7-bit addresses and an acknowledge bit after each byte C. Long-distance transmission D. No addressing needed Answer: B. I2C supports many devices with addresses and ACK; it is slow and short-distance (limits). (Key point: I2C features) ## Related in Embedded System - [Arbitration and memory-mapped vs standard I/O](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aarbitration-memory-mapped-io) — Embedded System, chapter 5 - [Control methods for interface communication](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Ainterfacing-control-methods) — Embedded System, chapter 5 - [Daisy-chain arbitration](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Adaisy-chain-arbitration) — Embedded System, chapter 5, asked 5× - [Priority arbitration](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Apriority-arbitration) — Embedded System, chapter 5, asked 2× - [Priority and daisy-chain arbitration briefly](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aarbitration-priority-daisy-brief) — Embedded System, chapter 5 - [Priority arbitration vs daisy chain](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Apriority-arbitration-vs-daisy) — Embedded System, chapter 5 ## Related in other subjects - [Control system and its significance in engineering](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Awhat-is-cs-significance) — Control Systems, chapter 1 - [Bus hierarchy and bus arbitration](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Abus-hierarchy-arbitration) — Computer Organization and Architecture, chapter 1 - [Types of bus arbitration](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Abus-arbitration) — Computer Organization and Architecture, chapter 1 - [Communication protocol and OSI architecture](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aprotocol-osi-architecture) — Telecommunications, chapter 8