I2C protocol

About I2C

I2C Philips was the first company in 1982 A two-way two-wire serial bus protocol developed in . It only needs two signal lines to complete the information exchange , So far, there have been 100kHz、400kHz、1MHz、3.4MHz、5MHz Five communication rates . The final communication rate depends on the peripheral rather than the host chip .

I2C The signal line

SCL Clock line

SCL The clock line determines the communication rate , The higher the frequency is. , The faster the transmission rate , Its presence High voltage usually ,SDA Line data valid .

SDA cable

SDA The data line determines what data to transmit , High level means 1, Low level means 0. stay SCL During high level ,SDA Must be stable .

I2C sequential

• Start flag

  SCL High voltage usually ,SDA Switch from high level to low level

• End mark

  SCL High voltage usually ,SDA Switch from low level to high level
  

• Answer flag

  SCL At high power level ,SDA keep Low level

• Non response flag

  SCL At high power level ,SDA keep High level
  

• Waiting for an answer

  And answer / Same as non response , It's just a SCL Set high , Release SDA See the level of the slave

about I2C The temporal , Something to watch out for ：

1. GPIO initialization （ Hardware I2C The reuse open drain mode should be strictly used , Prevent large current backflow , The software can use the ordinary push-pull output mode , But when switching between output and input modes , Do not operate the high and low levels of the pins , In order to avoid unnecessary level ）
2. I2C The calculation of reading and writing speed should be determined MCU Clock speed 、 The maximum rate that the slave device can accept