[communication protocol] UART, I2C, SPI review

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Preface ： Communication basis

One 、UART(Universal Asynchronous Receiver/Transmitter)

Two 、I2C

3、 ... and .SPI

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Preface ： Communication basis

Before understanding the communication protocol , First of all, we need to understand the basics of communication

        1. Parallel and serial

                Parallel communication : Multi track data cable , Transfer data side by side , There's a lot of interference , Take up more resources

                serial communication : A data cable , One bit One bit Send data , Little interference , Less resources

        2. Simplex and duplex

                Simplex ： One way transmission of data , The transmission direction cannot be changed

                Duplex ：1. Half duplex ： Both sides of communication can transmit data to each other , But it cannot be transmitted at the same time ( Do not send and receive at the same time )

                            2. full duplex ： Both sides of communication can transmit data to each other at the same time ( Send and receive at the same time )

        3. Baud rate (bit per second)

                Serial communication rate , Company bps, That is... Transmitted per second bit digit

         4. Synchronous and asynchronous

                asynchronous communication ： The clocks of communication parties are not synchronized , Generally, data is transmitted according to character frame (5-8 position ) Send data in bits , Low efficiency , For low-speed communication

                Synchronous communication ： Communication dual engine clock synchronization , According to the beat of the clock , Send in block bits , More efficient , The structure is more complicated , For high-speed communication

Tips ： The following is the main body of this article , The following cases can be used for reference

One 、UART(Universal Asynchronous Receiver/Transmitter)

        1. Interface mode ： Half duplex / full duplex asynchronous communication , Single double three wire

        2. Communication process ： The bus is idle , At high level

                              Communication begins ： Send data in character frame format , Start low and then start high

                              Character frame ：1bit Start bit +5~8bit Data bits +1bit Parity bit ( not essential )+1bit or 2bit Stop bit

                                              Start bit : Pull the bus down , On behalf of communication start

                                              Stop bit ： Pull the bus up , Represents the end of the communication  

        3. characteristic : The electrical interface is not unified , Poor anti-interference ability , Short communication distance

        4.RS232 And RS485 standard

            annotation ：RS232 And RS485 It's just a rule UART Electrical interface standard of , It hasn't changed UART Sending and receiving timing

             RS232:

                Electrical protocol ： Logic “1”：-5~-15V, Logic “0”：+5~+15V

                Interface ：DB-9( The actual time is three wire system ：RXD,TXD,GND), full duplex

                 characteristic ： Short transmission distance 15m, High level value is easy to burn out the circuit , Prone to common mode interference , Poor anti noise ability

             RS485:

                 Electrical protocol ：  Logic “1”：2~ 6V, Logic “0”：-2~-6V , Differential line signal transmission ( That is, the voltage difference between the two lines 0/1)

                Interface ： Two wire system , Bus topology , Half duplex

                characteristic ： Allows the bus to connect multiple transceivers , Form similar I2C Device network

                            Anti noise , Long transmission distance 1500m

        

                

Two 、I2C

        1. Interface mode ： Half duplex , Sync , Two wire system (SDA,SCLK)

        2. Communication process ： The host sends the start signal ,

                              Host send 7bit Slave address +1bit Transmission relation bit of

                              The addressed slave sends ACK Reply back to the host

                              The transmitter sends a byte of data

                              The receiver accepts data , And send the ACK The reply

                               ....

                              When the communication is complete , The host sends a stop signal

                    Idle ：SDA,SCLK pull up

                    Start signal ： The host initiates ,SCLK At high level ,SDA From high to low

                    Byte transfer ： First high then low

                     ACK The reply ： Every time a byte is transferred , The receiver sends to 1bit The answer signal of It's a frame 9bit

                      The data transfer ：SCLK During low level , The transmitter is SDA send out 1bit data , period SDA Allowable change

                                        SCLK During high level , The receiver is in SDA Read 1bit data , period SDA No change is allowed

                      Stop signal ： The host initiates ,SCLK During high level ,SDA From low to high

                        

              3. characteristic ： Low communication distance , Low transmission rate , Can mount multiple devices , Multi host bus , With anti-collision detection , Arbitration function

             

3、 ... and .SPI

        1. Interface mode ： Full duplex synchronization ,

                                 At least four wires (SCLK,MOSI(Maste Ouput Slave Input),MISO,CS(Chip Slect))

        2. Communication process ：

                1. Addressing ： The host sends to the transmitter CS The signal

                2. The data transfer ： Byte transmission , First pass the high position, then the position

                3. No response signal is required , Start the next byte transfer directly

                4. Sending data ： At the edge of the clock line , send data

                5. Receive data ： Next edge , The receiver reads data

        

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