Communication bus protocol I ：UART

1. Communication basis

1.1 parallel , Serial

• Parallel transmission ： Data in groups , stay Simultaneous transmission on multiple parallel channels
• Serial transmission ： Use A data line , Transmit data bit by bit , A fixed length of data

1.2 Simplex , Duplex

• Simplex communication ： Only one party is allowed to transmit information to the other party , The other party cannot send back information . Like the TV remote control 、 Radio broadcast, etc , It's all simplex communication technology .
• Half duplex communication ： Data can be transmitted between the two sides , But at the same time, only one party can send it to the other Fang . For example, walkie talkie .
• Full duplex communication ： It refers to the ability to receive data while sending data , The two go hand in hand , Like the phone .

1.3 Sync , asynchronous

• asynchronous communication ： Both sides of the communication Use their own clocks , According to the agreed unified baud rate , Send and receive data . There may be some error in the clock frequency of both sides , Asynchronous communication a data frame is short , Low sending efficiency .
• Synchronous communication ： signal communication Both parties use clocks with the same frequency , The sender should send data at a fixed rhythm , The receiver should always be ready to receive data , After recognizing the preamble, we will start receiving data immediately . The synchronization data frame length is large , More efficient , It is more suitable for transmission with high speed requirements .

1.4 Baud rate

Baud rate ： The rate of serial communication , Unit is bps (bit per second), That is, how many binary bits can be transmitted per second . For example, it can transmit... Every second 9600 It's binary , The baud rate is 9600.

2. Uart Communication protocol

• Free bit ： When there is no data transmission on the data line , The data line remains high , That is, the idle bit is 1
• Start bit ： When starting data transfer , Data line from 1 become 0, Transmission start bit 0
• Data bits ： One time transmission 5~8 position , It is usually a transmission 8 position , That is, a byte. Starting low , Late onset high , For example, transmission 0x55, Corresponding binary 0 1 0 1 0 1 0 1, Send low order first （ Far right ） Of 1
• Inspection position ： Take up one bit, Use parity test , Check bits are optional
• Stop bit ： Indicates that one frame of data transmission is completed , Stop bit occupied 1~2bit
• uart Only one character can be transmitted at a time , If you need to transmit multiple characters , Then each character will follow the above frame format , transmitted
• Both sides of the communication , It must be set to the same baud rate , To communicate correctly

3. Hardware connection

• uart The hardware connection of is very simple , As shown in the figure above ： Sending of one party Tx Connect the receiving of the other party Rx, Ground wire GND Connect to .

---

Thank you for reading If there is an error Excuse me ！！！

---