Common Embedded Bus Protocols Explained

IIC Bus (Inter－Integrated Circuit)

I2C (Inter-Integrated Circuit), also known as IIC or I2C bus, is a serial communication protocol used to connect multiple devices over short distances. It was first introduced by Philips in 1982 and is now widely used for communication between embedded systems, sensors, memory, and other peripheral devices. Here are some detailed information about I2C:

Physical Layer Characteristics

Two-wire System: The I2C bus uses two lines, SDA (Serial Data Line) and SCL (Serial Clock Line).

SDA Line: The line for data transmission, which can be shared by multiple devices.

SCL Line: The line for transmitting clock signals, used to synchronize data transmission.

Working Principle

Start and Stop Conditions: Communication begins with a start condition and ends with a stop condition.

Start Condition: The SDA line switches from high to low while the SCL line remains high.

Stop Condition: The SDA line switches from low to high while the SCL line remains high.

Data Transmission: Data transmission always occurs on the rising or falling edge of SCL, and the level changes on SDA are only valid when SCL is low.

Each data bit on the data line is transmitted within one clock cycle of SCL, starting with the high bit followed by the low bit.

After each byte transmission, there can be an ACK (acknowledgment) bit.

Address Frame: At the start of communication, the master device sends a frame containing a 7-bit or 10-bit address to select the slave device for communication.

Device Roles

Master Device: The device that controls the I2C bus, responsible for initiating and stopping communication and sending address frames.

Slave Device: Responds to commands from the master device and sends or receives data as needed.

Clock Frequency

The clock frequency of the I2C bus is variable, allowing adjustments based on system requirements. Typically, the clock frequency can be set from several hundred kilohertz to several megahertz.

Advantages and Applications

Simple and Flexible: The I2C communication protocol is relatively simple and easy to implement, suitable for scenarios involving multiple devices.

Suitable for Short-Distance Communication: Due to its two-wire system and synchronous transmission, I2C is suitable for short-distance communication, typically within a few meters.

Widely Used: Commonly used to connect sensors, memory, displays, and other peripheral devices, especially in embedded systems and the Internet of Things.

SPI Bus (Serial Peripheral Interface)

SPI (Serial Peripheral Interface) is a synchronous protocol used for serial communication, typically for fast, full-duplex data transmission between microcontrollers and external devices. The SPI protocol supports point-to-point, point-to-multipoint, and multipoint-to-multipoint communication topologies, suitable for connecting various peripheral devices such as memory, sensors, displays, and other microcontrollers. Here are some key features and working principles of SPI:

Physical Connection

Signal Lines:

MOSI (Master Out Slave In): The line for data sent from the master device to the slave device.

MISO (Master In Slave Out): The line for data sent from the slave device to the master device.

SCLK (Serial Clock): The synchronous clock line used to drive data transmission.

SS/CS (Slave Select/Chip Select): The line used to select the slave device for communication, allowing multiple slave devices to be connected.

Full-Duplex Communication:

SPI allows simultaneous data transmission on both MOSI and MISO lines, achieving full-duplex communication.

Working Principle

Frame Structure:

Data is transmitted in frames, each frame typically includes one or more data bits and a clock bit.

Clock Polarity and Phase:

Clock Polarity (CPOL): Defines whether SCLK is high or low when idle.

Clock Phase (CPHA): Defines when data is sampled, either on the rising or falling edge.

Data Transmission:

Data is typically transmitted on the rising or falling edge of SCLK.

The master device generates the clock signal, and the slave device samples and sends data according to the clock signal.

Master-Slave Relationship:

In SPI communication, there is usually one master device and one or more slave devices. The master device is responsible for initiating communication, while the slave device responds to commands from the master device.

Speed Adjustment:

The clock frequency of SPI can be adjusted through software or hardware configuration to meet the needs of different devices.

Advantages and Applications

High-Speed Data Transmission: SPI communication is typically faster than other serial communication protocols like I2C, suitable for applications requiring high-speed data transfer.

Suitable for Short Distances: SPI communication is generally suitable for relatively short-distance communication, typically within a few meters.

Simple Hardware Connection: SPI communication uses a few signal lines, making hardware connections relatively simple.

Multi-Device Support: SPI allows connecting multiple slave devices by selecting different SS/CS lines to communicate with specific devices.

I2S Bus (Inter-IC Sound Bus)

I2C (Inter-Integrated Circuit) is a serial communication protocol used to connect multiple devices over short distances, originally introduced by Philips and now maintained by NXP Semiconductors. The I2C communication protocol is widely used for communication between embedded systems, sensors, memory, and other peripheral devices. Here are some detailed information about I2C:

Physical Layer Characteristics

Two-wire System: The I2C bus uses two lines, SDA (Serial Data Line) and SCL (Serial Clock Line).

SDA Line: The line for data transmission, which can be shared by multiple devices.

SCL Line: The line for transmitting clock signals, used to synchronize data transmission.

Working Principle

Start and Stop Conditions: Communication begins with a start condition and ends with a stop condition.

Start Condition: The SDA line switches from high to low while the SCL line remains high.
Stop Condition: The SDA line switches from low to high while the SCL line remains high.

Data Transmission: Data transmission always occurs on the rising or falling edge of SCL, and the level changes on SDA are only valid when SCL is low.

Each data bit on the data line is transmitted within one clock cycle of SCL, starting with the high bit followed by the low bit.
After each byte transmission, there can be an ACK (acknowledgment) bit.

Address Frame: At the start of communication, the master device sends a frame containing a 7-bit or 10-bit address to select the slave device for communication.

Device Roles

Master Device: The device that controls the I2C bus, responsible for initiating and stopping communication and sending address frames.

Slave Device: Responds to commands from the master device and sends or receives data as needed.

Clock Frequency: The clock frequency of the I2C bus is variable, allowing adjustments based on system requirements. Typically, the clock frequency can be set from several hundred kilohertz to several megahertz.

Advantages and Applications

Simple and Flexible: The I2C communication protocol is relatively simple and easy to implement, suitable for scenarios involving multiple devices.

Suitable for Short-Distance Communication: Due to its two-wire system and synchronous transmission, I2C is suitable for short-distance communication, typically within a few meters.

Widely Used: Commonly used to connect sensors, memory, displays, and other peripheral devices, especially in embedded systems and the Internet of Things.

CAN Bus (Controller Area Network)

CAN (Controller Area Network) is a serial communication protocol designed for highly reliable real-time communication. It was originally developed by Bosch in Germany in 1986, primarily for the automotive field, but is now widely used in other areas such as industrial control, aerospace, and other embedded systems. Here are some detailed information about the CAN protocol:

Physical Layer Characteristics

Two-wire System: The CAN bus uses two lines, CAN_H and CAN_L, forming a differential signal pair.

Differential Signal: CAN uses differential signaling to enhance interference resistance and noise tolerance.

Bus Topology: The CAN bus supports a multi-master and multi-slave topology, forming a bus network.

Working Principle

Frame Structure: CAN communication uses a frame structure, divided into standard and extended frames. Each frame contains an identifier, control bits, data fields, and checksum fields.

Communication Method: CAN supports distributed communication with multiple masters, allowing any node to send messages.

Collision Avoidance: CAN uses the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism to prevent data collisions.

Arbitration: When multiple nodes send messages simultaneously, the arbitration mechanism on the CAN bus determines which message has a higher priority, allowing only the highest priority message to be sent successfully.

Device Roles

CAN Node: Can be a master node (typically a control unit) or a slave node (typically sensors, actuators, etc.).

Master Controller: Responsible for controlling the entire network, including frame transmission and arbitration.

Communication Rate: The communication rate of the CAN bus can be adjusted based on application needs, with typical rates including 100 Kbps, 250 Kbps, 500 Kbps, and 1 Mbps.

Advantages and Applications

Real-Time Performance: The CAN protocol has low latency and high real-time performance, suitable for applications with strict timing requirements.

Robustness: Differential signaling, arbitration mechanisms, and error detection and handling make the CAN protocol perform excellently in noisy electromagnetic environments.

Suitable for Large-Scale Systems: The CAN bus is suitable for connecting a large number of devices, such as multiple control units in automotive networks.

Widely Used: In addition to the automotive field, the CAN protocol is also widely used in industrial automation, medical devices, aerospace, and other fields.

👆Click to view video explanation👆

UART Bus (Universal Asynchronous Receiver Transmitter)

UART (Universal Asynchronous Receiver/Transmitter) is a common serial communication protocol used for transmitting data between computers, embedded systems, and other devices.UART is asynchronous, meaning data transmission does not rely on a shared clock signal.Here are some detailed information about the UART protocol:

Physical Layer Characteristics

Signal Lines: UART communication typically uses two lines, TX (transmit line) and RX (receive line).

Asynchronous Communication: Data transmission does not rely on a shared clock signal, but is determined by a combination of start bits, data bits, and stop bits to indicate the start and end of data.

Baud Rate: Baud rate indicates the number of bits transmitted per second, which is an important parameter in UART communication. Both sender and receiver must set the same baud rate.

Frame Structure

Start Bit: Logic 0, indicating the start of data.

Data Bits: Typical value is 8 bits, indicating the number of data bits for each character.

Parity Bit: Optional, used for error detection. Can be odd parity, even parity, or no parity.

Stop Bits: Typically 1 or 2 bits, used to indicate the end of data.

Working Principle

Sender:

Data is divided into frames, including start bits, data bits, parity, and stop bits.
Data starts sending from the least significant bit (LSB).
Start bit is 0, data bits are sent from least significant to most significant, parity is sent according to the set method, and finally the stop bit.

Receiver:

The receiver monitors the receive line throughout the baud rate.
When it detects the start bit of 0, it begins to read the data bits, followed by the parity bit and finally the stop bit.
The receiver uses the start bit, data bits, and stop bits to parse the received data.

Advantages and Applications

Simple: The UART protocol is relatively simple and easy to implement, suitable for simple communication between various embedded systems and devices.

Flexibility: As it is asynchronous communication, UART is suitable for serial communication between different devices without needing to share clock signals.

Suitable for Short Distances: Typically used for relatively short-distance communication, such as connections within PCBs or between devices.

Common Applications: UART is commonly used in serial communication, such as connecting computers with external devices, debugging and communication in embedded systems, etc.

– END –

Click the video below to follow our video account for exciting videos!

Add Assistant Get Study Notes

After adding, reply“Notes” to receive it faster~

Physical Layer Characteristics

Working Principle

Start and Stop Conditions: Communication begins with a start condition and ends with a stop condition.

Start Condition: The SDA line switches from high to low while the SCL line remains high.

Stop Condition: The SDA line switches from low to high while the SCL line remains high.

Device Roles

Clock Frequency

Advantages and Applications

Physical Connection

Working Principle

Advantages and Applications

Physical Layer Characteristics

Working Principle

Device Roles

Clock Frequency: The clock frequency of the I2C bus is variable, allowing adjustments based on system requirements. Typically, the clock frequency can be set from several hundred kilohertz to several megahertz.

Advantages and Applications

Physical Layer Characteristics

Working Principle

Device Roles

Communication Rate: The communication rate of the CAN bus can be adjusted based on application needs, with typical rates including 100 Kbps, 250 Kbps, 500 Kbps, and 1 Mbps.

Advantages and Applications

Physical Layer Characteristics

Frame Structure

Working Principle

Advantages and Applications

Related posts

Leave a Comment Cancel reply