Main features of IIC bus / communication process / read / write process

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Learning microcontroller must be some bus learning , Today, let's talk about IIC Bus , It is a kind of bus that we often use , This bus type was designed by Philips semiconductor in the early 1980s .

IIC What is a bus

IIC It is mainly used to connect the whole circuit （ICS）,IIC It's a multidirectional control bus , In other words, multiple chips can be connected to the same bus structure , At the same time, each chip can be used as the control source of real-time data transmission . This way simplifies the signal transmission bus interface .IIC There are only two bidirectional signal lines , One is the data line SDA, One is the clock line SCL.

IIC The main features

• It has multi-function , The module can be used as both master device and slave device .

• IIC Main equipment function , It mainly generates clock signals （ Start signal and stop signal ）.

• IIC Slave device functions , programmable IIC Address detection , Stop bit detection .

• Support different communication speeds , Standard speed （ The highest speed 100kHZ）, Fast （ The highest 400kHZ）.

IIC Communication process

In main mode ,IIC The interface starts data transmission and generates a clock signal . Serial data transmission always starts with a start condition and ends with a stop condition . Both start and stop conditions are generated and controlled by software in main mode .

When in slave mode ,IIC The interface can identify its own address （7 Bits or 10 position ） And the address broadcast on the data bus （ Like everyone has a different identity ID, Answer whatever you call ）, At the same time, the software can control to turn on or prohibit the identification of broadcast call address .

The data and address are in accordance with 8 Bits per byte , High in the former . Following the starting condition 1 perhaps 2 One byte is the address （7 The bit mode is 1 Bytes ,10 The bit mode is 2 Bytes ）. Addresses can only be sent in main mode . In one byte transmission 8 The ninth clock period after the first clock , After receiving from the mode, you must return a ACK To the transmitter , This is the only way to transmit data .

remind ： stay IIC Idle ,SDA、SCL Keep it high .

Start signal ： In the clock SCL Keep it high , then SDA The data line changes from high level to low level, indicating the start signal .

Stop signal ： In the clock SCL Keep it high , then SDA The data line changes from low level to high level, indicating the stop signal .

Answer signal ： The host has sent a message 8 After bit data , Will wait for the answer from the slave ; One ACK The signal ,SDA Will pull down .

Each byte must be guaranteed to be 8 Bit length . When data is transmitted , Send the highest bit first （MSB）, Each transmitted byte must be followed by a reply bit （ That is, a frame has 9 position ）. If the response signal from the slave is not received within a period of time , It is automatically considered that the slave has correctly received the data .

stay IIC When the bus transmits data , When the clock signal is high , The data on the data line must be stable , Only when the signal on the clock line is low , The high level or low level state of the data line is allowed to change , Otherwise, the data transmission fails .

IIC Communication process

IIC The process of reading and writing , From the perspective of the Lord .

With AT24C02 And 2440 Connect IIC signal communication ,AT24C02 For from ,2440 Mainly .

AT24C series EEPROM The fixed part of the chip is 1010,A2,A1,A0 After the pin is connected to the high and low level, it is determined 3 Bit code , formation 7 The bit code is the address code of the device .

Last R/W It means whether to read or write ,0 To write ,1 For readout .

IIC read

The single chip microcomputer sends the signal of the device first 7 Bit address code and write direction bit “0”（“ Fake writing ”）, Release after sending SDA Line and in SCL The first... Is generated on the line 9 Clock signals . After confirming that the selected memory device is its own address , stay SDA A reply signal is generated on the line in response .

then , Send another byte of the first address of the memory area of the device to be read , After receiving the response , The MCU should repeat the start signal once and send out the device address and reading direction bit （“1”）, After receiving the device response, the data bytes can be read out , Every byte read , MCU should reply to the response signal . When the last byte of data is read , The MCU should return with “ Non response ”（ High level ）, And send a termination signal to end the readout operation .

  random block read

IIC write in

When the MCU performs write operation , First send the... Of the device 7 Bit address code and write direction bit ”0”（ common 8 position , A byte ）, Release after sending SDA Line and in SCL The first... Is generated on the line 9 Clock signals . After confirming that the selected memory device is its own address , stay SDA A reply signal is generated on the line as a response , After receiving the response, the single chip microcomputer can transmit data . When transmitting data , The MCU first sends a byte of the first address written into the memory , After receiving the response from the memory device , The single chip microcomputer sends data bytes one by one , But after each byte is sent, you have to wait for a reply .AT24C The serial on-chip address is automatically added after receiving each data byte address 1, On chip “ Number of bytes loaded at a time ” Within limits , Just enter the first address . The number of bytes loaded exceeds that of the chip “ Number of bytes loaded at a time ” when , The data address will “ Scroll up ”, The previous data will be overwritten .

  Byte write

  Page write

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