Advanced SPI Communication Techniques: From Four-Wire to Quad SPI, Daisy Chain Solutions to Double Your Project Speed!

1. Independent Chip Select (Standard Multi-Slave Mode)

Solution Description: Each slave device is assigned an independent SS (chip select) line, and the master device activates the target slave by pulling down the corresponding SS line.Advantages:

• Each slave is independently controlled, and communication does not interfere with each other.

• Supports full-duplex high-speed transmission.Disadvantages:

• The number of slaves is limited by the number of GPIOs on the master device.Application Scenarios:

• A small number of high-speed devices (e.g., the master connects to both SPI Flash and a display).Connection Diagram:

Master Device  SCLK ──┬── SCLK (Slave 1)         └── SCLK (Slave 2)  MOSI ──┬── MOSI (Slave 1)         └── MOSI (Slave 2)  MISO ──┬── MISO (Slave 1)         └── MISO (Slave 2)  SS1 ──── SS (Slave 1)  SS2 ──── SS (Slave 2) 

2. Daisy Chain

Solution Description: Multiple slave devices are connected in a cascading manner, using only one shared SS line, with data flowing sequentially through each slave.Working Principle:

• When the master device sends data, the data enters the first slave through MOSI, and its MISO connects to the next slave’s MOSI, forming a chain structure.

• The data packet sent by the master device contains instructions for all slaves, with each slave reading its required data and passing subsequent data to the next level.Advantages:

• Saves GPIOs on the master device (only one SS line is needed).

• Simplifies wiring complexity.Disadvantages:

• Low communication efficiency (data must be passed sequentially).

• Slaves must support data forwarding functions (e.g., shift registers or specific protocols).Application Scenarios:

• LED driver chip cascading (e.g., WS2812B simulating SPI mode).

• Multi-channel ADC/DAC expansion (e.g., AD7793).Connection Diagram:

Master Device  SCLK ──── SCLK (Slave 1) ──── SCLK (Slave 2)  MOSI ─── MOSI (Slave 1)  MISO ←── MISO (Slave 1) ←── MOSI (Slave 2)  SS ────── SS (Slave 1) ────── SS (Slave 2) 

3. Bus Sharing (Broadcast Mode)

Solution Description: Multiple slaves share the MOSI, MISO, SCLK, and SS lines, and the master device simultaneously selects multiple slaves through the SS lines.Working Principle:

• The master device pulls down multiple SS lines to broadcast data to all selected slaves.

• Slaves must support “ignore non-target instructions” or identify their data through an address field.Advantages:

• Supports batch configuration of identical devices (e.g., multi-channel relay control).Disadvantages:

• Risk of data conflict (multiple slaves driving the MISO line simultaneously).

• Slaves must support address filtering or tri-state output.Application Scenarios:

• Sensor arrays for multi-channel synchronous control (e.g., industrial temperature control systems).

• Parallel configuration of multiple identical peripherals (e.g., motor driver chip DRV8837).

4. Tree Topology (Hybrid Mode)

Solution Description: Combines independent chip select and daisy chain to form a tree structure. For example, the master device controls multiple daisy chain branches through multi-level SS lines.Advantages:

• Strong scalability, supporting large-scale slave networks.Disadvantages:

• Logical control is complex, requiring hierarchical management of SS signals.Application Scenarios:

• Distributed sensor networks in industrial automation.

• Multi-level cascading display panels (e.g., advertising screen control systems).

Typical Application Cases

Case 1:SPI Daisy Chain Driving LED Array

Hardware Configuration:

• Master Control: STM32F4

• Slave: 74HC595 Shift Register (cascaded 3 pieces)Implementation Plan:

1. The master control sends 3 bytes of data sequentially through MOSI (each byte corresponds to one 74HC595).

2. Data enters the first 74HC595’s MOSI and is passed to the next piece through internal shifting.

3. The master pulls up the SS line, triggering all 74HC595s to latch outputs simultaneously, controlling 24 LEDs.Advantages:

• Only 3 lines (SCLK, MOSI, SS) are needed to control a large number of LEDs, saving GPIO resources.

Case 2:QSPI Expansion for Large Capacity Storage

Hardware Configuration:

• Master Control: ESP32-S3 (supports QSPI mode)

• Memory: W25Q128JV (128Mbit Quad SPI Flash)Implementation Plan:

1. The master control transmits data through IO0-IO3 in four lines, with a clock frequency increased to 80 MHz.

2. Single transmission of 32-bit address + data, with a rate of up to 320 Mbps (4 times that of standard SPI).

3. Enables HOLD and WP lines for write protection and pause operations.Advantages:

• High-speed storage of firmware or image data, suitable for IoT device OTA upgrades.

Case 3:Multi-Sensor Synchronous Acquisition

Hardware Configuration:

• Master Control: Raspberry Pi

• Slaves: BMI160 (6-axis IMU), BME280 (temperature, humidity, and pressure sensor)Implementation Plan:

1. The master selects BMI160 and BME280 through independent SS lines.

2. In full-duplex mode, the master reads acceleration data from BMI160 while sending configuration commands to BME280.

3. Uses SPI clock mode 0 (CPOL=0, CPHA=0) to ensure timing compatibility.Advantages:

• Parallel operation of multiple sensors improves system response speed.

SPI Design Considerations

1. Signal Integrity:

• For long-distance communication, buffers (e.g., SN74LVC245) or impedance matching resistors should be added.

• Avoid high SCLK frequencies that cause signal reflections (usually <10 MHz; reduce frequency for longer PCB traces).

Slave Conflict Handling:

• Only one slave is allowed to drive the MISO line on the bus; other slaves’ MISO must be set to high impedance.

Power and Ground Lines:

• To reduce noise, SPI signal lines should run parallel to power ground lines and minimize loop area.

Software Optimization:

• Use DMA transmission to reduce CPU usage (e.g., STM32’s SPI_DMA mode).

• Detect transmission completion flags through interrupts or polling (e.g., SPI_I2S_FLAG_RXNE).

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