SPI Protocol Communication Process Analysis: How Master and Slave Devices Conduct Data Transmission

# SPI Protocol Communication Process Analysis: How Master and Slave Devices Exchange Data

## 1. Introduction

### 1.1 What is SPI Protocol?

SPI (Serial Peripheral Interface) protocol is a fully-duplex communication protocol used to connect microcontrollers with external devices for high-speed data transmission. It consists of four wires: clock line (SCK), master output slave input line (MOSI), master input slave output line (MISO), and slave select line (SS).

### 1.2 The Basic Principle of SPI Communication

SPI communication is synchronized by the clock signal generated by the master device to transfer data between the master and slave devices. The master device controls the frequency of the clock signal and the sequence of data transmission, while the slave device receives and sends data based on the clock signal. SPI protocol supports full-duplex communication, capable of high-speed data transmission, making it suitable for scenarios with high communication speed requirements. SPI protocol is typically used in embedded systems, industrial control devices, and other fields.

# 2. SPI Protocol Communication Methods

### 2.1 Roles of Master and Slave Devices

#### 2.1.1 Master Device

The master device is the one that initiates communication and controls data transmission in SPI communication. The master device uses the clock signal to synchronize data transmission and is responsible for selecting the communication slave device. The master device starts data transmission by selecting the slave device and using specific logical signals.

##### *.*.*.* Principle of Master Device Operation

The master device controls the method of data transmission by setting the polarity (CPOL) and phase (CPHA) of the clock and data signals. At the beginning of communication, the master device first pulls the slave select signal (SS) low to select a specific slave device, then begins generating the clock signal and transmits data according to the changes in the clock signal.

import spidev

spi = spidev.SpiDev()
spi.open(0,0)
spi.max_speed_hz = 1000000

def transfer_data(data):
     spi.xfer2([data])

##### *.*.*.* Signal Transmission Between Master and Slave Devices

The master device sends data to the slave device via the MOSI (Master Out Slave In) line, while the slave device sends data back to the master device via the MISO (Master In Slave Out) line. The clock signal is generated by the master device and controls the timing of data transmission.

#### 2.1.2 Slave Device

The slave device is the one that receives data and responds to the master device's commands in SPI communication. The slave device cannot actively choose to communicate with the master device but can only passively receive and respond to data transmitted by the master device.

##### *.*.*.* Principle of Slave Device Operation

Upon receiving the master device's slave select signal, the slave device waits for the activation of the clock signal. Under the control of the clock signal, the slave device receives data sent by the master device and sends response data back to the master device via the MISO line.

import spidev

spi = spidev.SpiDev()
spi.open(0,0)
spi.max_speed_hz = 1000000

def receive_data():
     rx_data = spi.xfer2([0xFF])
     return rx_data[0]

##### *.*.*.* How Slave Devices Respond to Master Device's Commands

After receiving complete data, the slave device can execute corresponding operations based on the data content and send the execution results back to the master device via the MISO line. The slave device's response must be completed under the synchronization of the clock signal to ensure accurate data transmission.

# 3. Timing Diagram Analysis of SPI Communication

SPI (Serial Peripheral Interface) communication is a synchronous serial data communicatio