SPI protocol

About SPI

SPI It was first proposed by Motorola , At first there was no written standard . It is a serial peripheral interface （Serial Peripheral Interface） Abbreviation , It's a high speed 、 full duplex 、 Synchronous communication bus . And MCU Communication only takes up four pins , Namely ：MOSI、MISO、SCK、CS.

SPI Hardware layer

• MOSI：master out slave in Abbreviation , Both host output and slave input
• MISO：master in slave out Abbreviation , Both host input and slave output
• SCLK：serial clock Abbreviation , Clock line
• CS：chip select Abbreviation , Existing line selection , Sometimes it is written as NSS

SPI Protocol layer

• Clock polarity CPOL Refer to SPI When communication is idle ,SCLK The level signal of the signal line .
  • CPOL=0 when ,SCLK Low level in idle state
  • CPOL=1 when ,SCLK High level in idle state
• Clock phase CPHA It refers to the sampling time of data .
  • When CPHA=0 when ,MOSI or MISO The signal line on the data line will be at SCLK Clock line “ Odd edge ” Be sampled
  • When CPHA=1 when ,MOSI or MISO The signal line on the data line will be at SCLK Clock line “ Even edge ” Be sampled
    
    
    The mode selection should be determined according to the slave chip

SPI Points that the agreement should pay attention to

1. Before the slave machine is used, it is necessary to CS The film selection line is pulled down , Must be raised after use
2. Pay attention to the validity of data , Whether the data is sent on the rising edge or the falling edge , Whether the data is received on the rising edge or the falling edge