SPI and I2C are key serial communication protocols used in embedded systems. They enable devices to talk to each other, but in different ways. SPI is faster and uses separate lines for data, while I2C uses a shared bus with fewer wires.

Understanding these protocols is crucial for designing efficient embedded systems. SPI is great for high-speed data transfer, while I2C shines in systems with limited pins. Both have their strengths and are widely used in various applications.

SPI Protocol

Architecture and Data Transmission

• SPI (Serial Peripheral Interface) is a synchronous serial communication protocol that enables high-speed data transfer between a master device and one or more slave devices
• Employs a master-slave architecture where the master initiates and controls the communication with the slave devices
• Data transmission occurs over two separate lines:
  • MOSI (Master Out Slave In) carries data from the master to the slave
  • MISO (Master In Slave Out) carries data from the slave to the master

Clock and Slave Selection

• SCK (Serial Clock) is generated by the master device and synchronizes the data transfer between the master and slave devices
  • The clock signal determines when data is sampled and shifted on the MOSI and MISO lines
• SS (Slave Select) is an active-low signal used by the master to select the slave device it wants to communicate with
  • Each slave device has its own dedicated SS line connected to the master
  • The master asserts the SS line of the desired slave to initiate communication and de-asserts it when the communication is complete

Advantages and Applications

• SPI offers full-duplex communication, allowing simultaneous data transmission and reception
• Provides high data transfer rates compared to other serial protocols (I2C)
• Widely used in various applications such as sensors, memory devices (EEPROM, Flash), display controllers, and peripheral devices

I2C Protocol

Bus Architecture and Data Transmission

• I2C (Inter-Integrated Circuit) is a synchronous serial communication protocol that enables communication between multiple devices using a shared bus
• Utilizes a two-wire bus architecture consisting of:
  • SDA (Serial Data) line for bidirectional data transfer
  • SCL (Serial Clock Line) for synchronizing the data transfer
• Devices connected to the I2C bus can act as either a master or a slave
  • The master initiates and controls the communication, while the slaves respond to the master's requests

Addressing and Multi-Master Support

• Each device on the I2C bus has a unique address, allowing the master to selectively communicate with specific devices
  • The address is typically 7 bits long, providing support for up to 128 devices on the same bus
• I2C supports multi-master functionality, allowing multiple master devices to coexist on the same bus
  • Arbitration mechanism is employed to handle potential conflicts when multiple masters attempt to access the bus simultaneously
  • The master with the highest priority gains control of the bus

Advantages and Applications

• I2C requires only two wires (SDA and SCL) for communication, making it suitable for systems with limited pin count
• Supports a wide range of data transfer rates, from low-speed (10 kHz) to high-speed (3.4 MHz) modes
• Commonly used in various applications such as sensor networks, real-time clocks (RTC), EEPROMs, and power management ICs