I2C Interview Questions

I2C (Inter-Integrated Circuit) is a widely used serial communication protocol in embedded systems. It enables efficient data transfer between microcontrollers and peripheral devices by utilizing a shared bus. With I2C, multiple devices can be connected to the same bus, allowing for easy expansion and integration. The protocol uses two lines, SDA (Serial Data) and SCL (Serial Clock), to transmit and receive data. I2C is known for its simplicity, low pin usage, and support for low-power devices. It finds applications in various fields, including sensor interfaces, memory modules, real-time clocks, and more.

I2C Interview Questions :

Q1 : What is I2C, and how does it work?

Ans : I2C (Inter-Integrated Circuit) is a two-wire serial communication protocol developed by Philips Semiconductors for communicating between integrated circuits. It uses a clock signal (SCL) and a data signal (SDA) for communication and allows multiple devices to be connected to the same bus. Each device is identified by a unique address, and data is transferred in packets of 8 bits with ACK or NACK bits.

Q2 : What are the advantages of using I2C over other communication protocols?

Ans : Some advantages of using I2C over other communication protocols include its simplicity, low power consumption, low cost, and ability to support multiple devices on the same bus.

Q3 : What are the limitations of I2C?

Ans : Some limitations of I2C include its slow speed compared to other communication protocols like SPI, its limited range due to its two-wire nature, and the potential for signal integrity issues if the bus is not properly terminated.

Q4 : How many devices can be connected to an I2C bus?

Ans : The number of devices that can be connected to an I2C bus depends on the available address space.

1. 7-bit I2C can address 112 unique devices (excluding reserved addresses).
2. 10-bit I2C can address 1008 unique devices.

Q5 : What are some advanced features of I2C, and how are they used?

Ans : Some advanced features of I2C include clock stretching, multi-master support, and arbitration. Clock stretching allows a slave device to hold the clock line low to pause communication temporarily. Multi-master support allows multiple master devices to share control of the bus, while arbitration is used to resolve conflicts if two or more masters attempt to control the bus at the same time. These features are used to improve the reliability and efficiency of I2C communication in complex systems.

Q6 : What is the difference between I2C standard mode and fast mode?

Ans : I2C standard mode operates at a maximum frequency of 100 kHz, while fast mode operates at a maximum frequency of 400 kHz. Fast mode allows for faster data transfer rates but requires stronger pull-up resistors due to the higher data rate.

Q7 : How is clock synchronization maintained in I2C communication?

Ans : Clock synchronization in I2C is maintained through a combination of the clock signal and the ACK/NACK bits. The master device generates the clock signal and controls the timing of data transfer, while the slave devices respond to the clock signal and send ACK or NACK bits to indicate successful or failed data transfer.

Q8 : What are some common applications of I2C?

Ans : I2C is commonly used in a variety of applications, including sensors, displays, EEPROMs, and other peripheral devices. It is also used in system management applications such as power management and temperature monitoring.

Q9 : How do I2C devices communicate with each other?

Ans : I2C devices communicate with each other through a master-slave relationship. The master device initiates communication and sends commands or requests to the slave devices. The slave devices respond to the commands or requests by sending data back to the master device.

Q10 : How does I2C compare to other communication protocols such as SPI and UART?

Ans : I2C is slower than SPI but uses fewer pins, making it useful for applications with limited board space. UART is a point-to-point communication protocol, while I2C supports multiple devices on the same bus. Each protocol has its own advantages and limitations, and the choice of protocol depends on the specific application requirements.

Q11 : How is data transferred over the I2C bus, and what is the format of an I2C message?

Ans : Data is transferred over the I2C bus in packets of 8 bits. An I2C message typically consists of a start condition, slave address (with read/write bit), data bytes, and a stop condition. The master device initiates the communication by sending a start condition and then sends the slave address with the read/write bit to indicate the direction of data transfer. Data bytes are then transferred between the master and slave devices, with each byte followed by an ACK or NACK bit. The communication is terminated with a stop condition.

Q12 : How does I2C support different clock speeds and data rates?

Ans : I2C supports different clock speeds and data rates through different operating modes, such as standard mode, fast mode, and high-speed mode. In addition, I2C devices may support clock stretching, which allows the slave device to hold the clock line low to slow down the data transfer rate.

Q13 : How do I2C devices handle errors and retries during communication?

Ans : I2C devices may use various error detection and correction techniques, such as CRC checking, to ensure the integrity of the data being transferred. If an error occurs, the devices may attempt to retry the communication, or the master device may send a NACK bit to indicate that the communication has failed.

Q14 : What are some common issues that can arise when using I2C, and how can they be resolved?

Ans : Common issues with I2C include noise and signal integrity issues, addressing conflicts, and clock synchronization problems. These issues can be resolved by using appropriate pull-up resistors, terminating the bus properly, selecting unique device addresses, and carefully controlling the timing and frequency of data transfer.

Q15 : What is the difference between I2C and SMBus?

Ans : SMBus (System Management Bus) is a subset of I2C that defines a specific set of protocols and features for system management applications. SMBus devices are compatible with I2C devices, but SMBus includes additional features such as extended addressing and more robust error checking.

Q16 : How does clock stretching work in I2C communication?

Ans : Clock stretching is a feature of I2C that allows a slave device to hold the clock line low to slow down the data transfer rate. This can be used by the slave device to prevent the master from sending data too quickly, giving the slave device more time to process the data. The master device must wait for the clock line to go high again before continuing the communication.

Q17 : What is the maximum number of devices that can be connected to an I2C bus?

Ans : The maximum number of devices that can be connected to an I2C bus depends on the address space available. There are two address configurations in I2C 7 and 10 BIT.

7 BIT 

• A 7-bit address allows 128 possible addresses (0x00 to 0x7F in hexadecimal, or 0000 000 to 1111 111 in binary).

• However, some addresses are reserved, meaning not all 128 can be assigned to devices.

• Practical usable addresses: 112 (out of 128).

  • The first 8 addresses (0x00–0x07, i.e., 0000 XXX) are reserved.

  • The last 8 addresses (0x78–0x7F, i.e., 1111 XXX) are also reserved.

  • This leaves 112 valid device addresses.

10 BIT

• A 10-bit address expands the range to 1024 possible addresses (0x000 to 0x3FF in hex, or 0000 0000 00 to 1111 1111 11 in binary).

• Practically usable addresses: 1008 (some are reserved).

• More devices can be added, but many microcontrollers and devices still use 7-bit addressing for compatibility.

Q18 : What is the difference between an I2C master and an I2C slave?

Ans : An I2C master is a device that initiates communication on the bus and controls the timing of data transfer. A slave device responds to commands or requests from the master device and sends data back to the master device. Some devices, such as microcontrollers, can operate as both a master and a slave on an I2C bus.

Q19 : What is clock stretching and why is it used in I2C communication?

Ans : Clock stretching is a feature of I2C that allows a slave device to hold the clock line low to slow down the data transfer rate. This can be used by the slave device to prevent the master from sending data too quickly, giving the slave device more time to process the data. Clock stretching is particularly useful in applications where the slave device is slower than the master device or when the slave device needs more time to perform a task.

Q20 : What are some of the advantages and disadvantages of using I2C communication in embedded systems?

Ans : Some advantages of using I2C communication in embedded systems include its simplicity, low pin count, and support for multiple devices on the same bus. However, I2C communication may be slower than other communication protocols, and addressing conflicts and signal integrity issues can be a problem in complex systems.

Q21 : What is bus arbitration in I2C communication?

Ans : Bus arbitration is the process by which multiple devices on an I2C bus compete for control of the bus. If two or more devices try to communicate at the same time, a conflict can occur. The I2C bus has a built-in arbitration mechanism to resolve these conflicts and ensure that only one device is communicating on the bus at any given time.

Q22 : How does I2C bus arbitration work?

Ans : I2C bus arbitration works by having each device on the bus monitor the bus for activity. If two or more devices try to communicate at the same time, a collision occurs and the devices compare the data that they have sent to determine which device has priority. The device that sent the highest priority data wins the arbitration and continues communicating on the bus. The other device(s) will stop communicating and wait for another opportunity to communicate.

Q23 : What is priority in I2C bus arbitration?

Ans : Priority in I2C bus arbitration refers to the ability of a device to continue communicating on the bus if a conflict occurs. Devices with higher priority are able to continue communication while devices with lower priority are forced to stop communicating and wait for another opportunity to communicate. The priority of a device is determined by the content of the data that it is trying to send, with lower priority devices having to wait for higher priority devices to finish communicating.

Q24 : How are priorities assigned in I2C bus arbitration?

Ans : Priorities in I2C bus arbitration are assigned based on the content of the data being sent by each device. The content of the data is divided into two categories: the address and the data payload. The address has a higher priority than the data payload, and devices with lower addresses have higher priority than devices with higher addresses.

Q25 : What happens if two devices have the same priority in I2C bus arbitration?

Ans : If two devices have the same priority in I2C bus arbitration, a collision occurs and the devices compare the data that they have sent to determine which device has priority. The device that sent the highest priority data wins the arbitration and continues communicating on the bus. The other device(s) will stop communicating and wait for another opportunity to communicate.

Q26 : What are the reserved address in I2C ?

Ans :

Reserved 7-Bit Addresses

• Total Reserved Addresses (7-bit mode): 16 addresses (0x00–0x0F and 0x78–0x7F)
• Usable Addresses: 112 out of 128

Reserved Addresses in 10-Bit Mode

Certain addresses are reserved in 10-bit mode, similar to 7-bit mode.

• Total Reserved Addresses: 16 (0xF0 – 0xFF).
• Total Usable 10-bit Addresses: 1008 (0x000 – 0x3FF, excluding reserved ones).

Q27 : Explain the 10 BIT Addressing mode in I2C?

Ans :

• 10-bit I2C address consists of two bytes:

• • First byte (Prefix + Upper 2 bits of address + Read/Write bit)

  • Second byte (Remaining 8 bits of the address)

• First Byte (Prefix + Upper Address Bits + R/W Bit)

• • 1111 0 → Indicates a 10-bit address is being used. (Prefix)

  • A9 A8 → Upper 2 bits of the 10-bit address.

  • R/W → 0 for write, 1 for read.

• Second Byte (Lower 8 Bits of Address)

• • A7 - A0 → Lower 8 bits of the 10-bit address.

Important Links : 

1. Getting-Started-with-I2C:-A-Beginners-Guide
2. Getting-Started-with-I2C:-Hardware-Connection
3. Getting-Started-with-I2C:-What-is-Clock-Stretching
4. Getting-Started-with-I2C:-What-is-Bus-Arbitration
5. Getting-Started-with-I2C:-Code-Example