UART串口通讯原理

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通用异步收发传输器（Universal Asynchronous Receiver/Transmitter)，通常称作UART。它将要传输的资料在串行通信与并行通信之间加以转换。作为把并行输入信号转成串行输出信号的芯片，UART通常被集成于其他通讯接口的连结上。

特点

  • 只需要定义两个针脚
  • 异步通讯

如何工作

UART传输数据依靠的是UART总线，数据总线用于通过CPU，存储器或微控制器等其他设备将数据发送到UART。数据以并行形式从数据总线传输到发送UART。在发送UART从数据总线获得并行数据之后，它将添加起始位，奇偶校验位和停止位，从而创建数据包。接下来，数据包在Tx引脚上逐位串行输出。UART接收端则在其Rx引脚上逐位读取数据包。然后，接收UART将数据转换回并行形式，并删除起始位，奇偶校验位和停止位。最后，接收UART将数据包并行传输到接收端的数据总线。

  • 并行转换为串行
  • 添加起始位 奇偶效验位 停止位，打包
  • Tx引脚逐位输出
  • Rx接收端读取数据包
  • 解包

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MicroPython-UART

文档参考：https://docs.micropython.org/en/latest/library/pyb.UART.html#pyb-uart

例子

创建和初始化UART对象

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from pyb import UART

uart = UART(1, 9600)                         # init with given baudrate
uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters
# Bits can be 7, 8 or 9. Parity can be None, 0 (even) or 1 (odd). Stop can be 1 or 2.
# with parity=None, only 8 and 9 bits are supported. With parity enabled, only 7 and 8 bits are supported.

初始化分别设置传输位，校验位，停止位

UART读写操作

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uart.read(10)       # read 10 characters, returns a bytes object
uart.read()         # read all available characters
uart.readline()     # read a line
uart.readinto(buf)  # read and store into the given buffer
uart.write('abc')   # write the 3 characters

字符单独读写
uart.readchar()     # read 1 character and returns it as an integer
uart.writechar(42)  # write 1 character

检查是否有读写数据
uart.any()          # returns the number of characters waiting

方法

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UART.init(baudrate, bits=8, parity=None, stop=1, *, timeout=0, flow=0, timeout_char=0, read_buf_len=64)¶
  • Baudrate 波特率
  • bits 数据比特位数
  • parity 效验位
  • stop 停止位
  • flow 流控制
  • Timeout
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UART.deinit()

关闭UART总线

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UART.any()

返回等待读取的比特流

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UART.read([nbytes])

读取字符。nbytes设置每次读取最大字节数

若不设置nbytes，则返回最多字符

Note: for 9 bit characters each character takes two bytes, nbytes must be even, and the number of characters is nbytes/2

返回值：读取的比特流对象，超时返回None

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UART.readchar()

接受单个字符

返回值：返回一个字符，超时返回-1

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UART.readinto(buf[, nbytes])

从缓冲区读取比特流。nbytes指定读取最大比特

返回值：返回读取在buffer中的比特数。

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UART.write(buf)

Write the buffer of bytes to the bus. If characters are 7 or 8 bits wide then each byte is one character. If characters are 9 bits wide then two bytes are used for each character (little endian), and buf must contain an even number of bytes.

Return value: number of bytes written. If a timeout occurs and no bytes were written returns None.

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UART.writechar(char)

Write a single character on the bus. char is an integer to write. Return value: None. See note below if CTS flow control is used.

解包数据

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if uart_A.any():
    while uart_A.any():
        read_data = uart_A.read()
        read_data = read_data.decode('utf-8','ignore')  # 转为字符串
        if read_data[0] == 'b':                     # 切片
		   切片操作
           read_data = ''