1. The SPI protocol actually includes three protocol interfaces: Standard SPI, Dual SPI and Queued SPI, corresponding to 3-Wire, 4-Wire and 6-Wire respectively. The SPI we usually refer to is Standard SPI, which has 4 signal lines, namely CLK, CS, MOSI and MISO. The data line works in full duplex. Dual SPI is only for SPI Flash, not for all SPI peripherals. For SPI Flash, you can send a command byte to enter dual mode, so that MOSI becomes SIO0 (serial io 0) and MISO becomes SIO1 (serial io 1), so that 2 bits of data can be transmitted in one clock cycle, doubling the data transmission. Similarly, it can also be expanded, also for SPI Flash. Quad SPI Flash adds two IO lines (SIO2, SIO3), the purpose is to transmit 4 bits in one clock, and QSPI is the abbreviation of Queued SPI.
2. SPI communication usually involves four signal lines:
•SCK (Serial Clock): Clock signal, generated by the master device, used to synchronize data transmission.
•MOSI (Master Out Slave In): Data line output by the master device and input by the slave device.
•MISO (Master In Slave Out): Data line input by the master device and output by the slave device.
•CS (Chip Select): Chip select signal, used to select a specific slave device.
- SPI supports four operating modes, which are mainly determined by the clock polarity and phase: CPOL indicates the level of the clock idle state (0 or 1), and CPHA indicates that the clock edge (rising edge or falling edge) triggers data sampling.
(2) SPI advantages and disadvantages
The protocol is simple and easy to implement. It supports a high data transfer rate. It can send and receive data simultaneously. It requires four signal lines, which may not be very friendly to systems with limited resources. The SPI protocol itself does not support multi-master configuration.
3. QSPI usually has four modes:
•Single SPI (SPI): single data line mode, the same as traditional SPI.
•Dual SPI (DSPI): dual data line mode, using MOSI and MISO for bidirectional data transmission.
•Quad SPI (QSPI): quad data line mode, using four data lines for data transmission.
•Octal SPI (OSPI): eight data line mode, using eight data lines for data transmission.
QSPI signal line
•SCK (Serial Clock): clock signal, same as traditional SPI.
•IO0, IO1, IO2, IO3: four data lines, used for data transmission.
•CS (Chip Select): chip select signal, same as traditional SPI.
（2）QSPI still supports traditional SPI mode (mode 0 to mode 3), but in Quad mode, multiple bits can be transmitted per clock cycle, greatly improving the data transmission rate.
(3) QSPI advantages and disadvantages
By increasing the number of data lines, QSPI can significantly increase data transfer rates. QSPI is compatible with traditional SPI and can be flexibly switched on the same hardware. Although it adds data lines, QSPI still saves a lot of pins compared to parallel interfaces. The implementation of QSPI is more complex than traditional SPI and requires more hardware and software support. QSPI devices are generally more expensive than traditional SPI devices.
4. The data transfer rate of traditional SPI depends on the clock frequency and data bit width. Assuming a clock frequency of 10 MHz and 8 bits of data per transfer, the data transfer rate is 10 MB/s. QSPI has a data transfer rate of 40 MB/s
5. Application scenarios
SPI is suitable for low-speed, simple sensor interfaces. For small-capacity EEPROM or Flash memory, SPI is a suitable choice. SPI is commonly used to communicate with ADC and DAC chips.
QSPI is particularly suitable for fast read and write operations of large-capacity NOR Flash memory. In applications that require high-speed data transmission, such as boot loaders, operating system image loading, etc., QSPI provides higher performance. In industrial control systems, QSPI can provide faster data transmission rates and improve system response speed.