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1. Basic Knowledge of RS485 Communication

Therefore, subsequent engineers developed the RS-485 Communication Protocol. Compared with the RS-232-C interface, RS-485 has significant advantages in terms of transmission distance, anti-interference capability, multi-device communication and other aspects:

Differential Signal Transmission: RS-485 uses two signal lines (A and B) to represent "0" and "1" through voltage difference; this differential transmission method can effectively resist electromagnetic interference and ensure stable communication in noisy environments.

Multi-point communication: RS-485 allows multiple devices to be connected to the same bus. Typically, it supports 32 transmitters and 32 receivers, and even more devices can be connected via repeaters, which makes RS-485 highly suitable for scenarios requiring interconnection of multiple devices.

Long-distance transmission: The maximum transmission distance of RS-485 can reach 1200 meters (approximately 4000 feet), and the transmission speed is inversely proportional to the distance; as the transmission distance decreases, the data transmission rate can be increased, up to a maximum of 10 Mbps.

The communication process can be summarized as follows:

Master device data transmission: The master device transmits data via the RS-485 bus, which contains the address of the target slave device (slave device ID) and specific data; both line A (+ signal) and line B (- signal) are connected to all slave devices simultaneously.

Slave Listening: All slave devices monitor the data streams on lines A and B, and check the address information sent by the master device

Slave device selection: When a slave device detects that the address in the transmitted data packet matches its own slave device ID, it will receive the data packet and perform corresponding processing.

Slave Device Response: If the Communication Protocol requires the slave device to return data (such as status information, sensor data, etc.), the slave device will send response data to the master device; RS-485 is generally half-duplex, which means only one device can transmit data at the same time, so the transmission of response data needs to be carried out according to a predetermined timing sequence

2. Introduction to the MAX13487 Chip

3. Application Experiment

# Python env   : MicroPython v1.23.0
# -*- coding: utf-8 -*-        
# @Time    : 2024/9/23 下午3:53   
# @Author  : 李清水            
# @File    : main.py       
# @Description : UART类实验，RS485串口通信

# ======================================== 导入相关模块 =========================================

# 硬件相关的模块
from machine import UART, Pin
# 时间相关的模块
import time

# ======================================== 全局变量 ============================================

# UART配置参数
UART_TX_PIN : int = 16       # 发送引脚 (GPIO16)
UART_RX_PIN : int = 17       # 接收引脚 (GPIO17)
CONTROL_PIN : int = 18       # 收发控制引脚 (GPIO18)
BAUD_RATE   : int = 115200   # 波特率

# 设备ID
DEVICE_ID   : int = 1

# ======================================== 功能函数 ============================================

# ======================================== 自定义类 ============================================

# 自定义RS485通信类
class RS485Communication:
    """
    RS485通信类，用于通过RS485协议进行数据的发送和接收。

    该类实现了通过RS485协议的串口通信，包含了数据的发送、接收以及接收数据的处理。通过控制收发模式的引脚切换，
    可以在发送数据和接收数据之间切换。该类用于设备间的点对点通信或多点通信，确保数据流的正常传输和设备间的正确通信。

    Attributes:
        uart (UART): 串口对象，表示通过串口进行数据的发送和接收。
        device_id (int): 设备的唯一标识ID，用于区分不同设备之间的通信数据。
        control_pin (Pin): 控制引脚，用于切换收发模式。当发送数据时，将控制引脚设置为发送模式；接收数据时，设置为接收模式。

    Methods:
        send_data(data: str) -> None:
            发送数据，将设备ID与待发送数据一起发送，并切换到发送模式。

        receive_data() -> Union[bytes, None]:
            接收数据，检查是否有待接收的数据，并返回接收到的数据。如果没有数据，则返回None。

        process_received_data(received: bytes) -> None:
            处理接收到的数据。将数据解码并与设备ID进行比较，如果数据属于当前设备，则进行处理；否则忽略。
    """

    def __init__(self, uart: UART, device_id: int, control_pin: int):
        """
        初始化RS485通信对象。

        通过指定的串口对象、设备ID和控制引脚初始化RS485通信对象。

        Args:
            uart (UART): 串口对象，使用指定的UART端口进行数据传输。
            device_id (int): 设备的ID，用于标识该设备。
            control_pin (int): 收发控制引脚，用于切换串口收发模式。
        """
        # 设置串口对象
        self.uart = uart
        # 设置设备ID
        self.device_id = device_id
        # 设置收发控制引脚
        self.control_pin = Pin(control_pin, Pin.OUT)
        # 初始为接收模式
        self.control_pin.value(0)

    def send_data(self, data: str) -> None:
        """
        发送数据。

        通过串口发送带设备ID的数据，并切换收发控制引脚为发送模式。

        Args:
            data (str): 待发送的数据。

        Returns:
            None
        """

        # 设置为发送模式
        self.control_pin.value(1)
        # 添加设备ID和换行符
        message = f"{self.device_id}:{data}\r\n"
        # 发送数据
        self.uart.write(message)
        # 等待数据发送完成
        time.sleep(0.1)
        # 切换回接收模式
        self.control_pin.value(0)

    def receive_data(self) -> bytes:
        """
        接收数据。

        检查是否有可接收的数据，若有则读取数据。

        Returns:
            bytes: 接收到的数据，如果没有数据则返回 None。
        """

        # 检查是否有可接收的数据
        if self.uart.any():
            # 读取接收到的数据
            return self.uart.read()
        # 如果没有数据，返回None
        return None

    def process_received_data(self, received: bytes) -> None:
        """
        处理接收到的数据。

        将接收到的字节数据解码并根据设备ID进行处理。如果接收到的数据不是自己的ID，
        将打印该数据。若接收的数据格式不正确，则忽略。

        Args:
            received (bytes): 接收到的字节数据。

        Returns:
            None

        Raises:
            ValueError: 如果数据格式不正确，抛出ValueError异常。
        """

        # 解码数据并去除空格
        decoded_data = received.decode('utf-8').strip()
        # 按行分割数据，处理每一条消息
        messages = decoded_data.split('\r\n')

        # 遍历消息
        for msg in messages:
            # 如果消息不为空，进行处理
            if msg:
                # 分割设备ID和消息
                try:
                    sender_id, message = msg.split(':', 1)
                    # 如果发送者ID不是自己的ID
                    if sender_id != str(self.device_id):
                        # 打印接收到的消息
                        print("Received:", message)
                except ValueError:
                    # 如果数据格式不正确，忽略该消息
                    print("Received invalid message format:", msg)

# ======================================== 初始化配置 ==========================================

# 上电延时3s
time.sleep(3)
# 打印调试消息
print("FreakStudio: RS485 Communication with PC Demo")

# 创建串口对象，设置波特率为115200
uart: UART = UART(0, BAUD_RATE)
# 初始化uart对象，波特率为115200，数据位为8，无校验位，停止位为1
# 设置接收引脚为GPIO9，发送引脚为GPIO8
# 设置串口超时时间为100ms
uart.init(baudrate  = BAUD_RATE,
          bits      = 8,
          parity    = None,
          stop      = 1,
          tx        = UART_TX_PIN,
          rx        = UART_RX_PIN,
          timeout   = 100)

# 创建RS485通信对象
rs485: RS485Communication = RS485Communication(uart, DEVICE_ID, CONTROL_PIN)

# ========================================  主程序  ===========================================

# 循环执行
while True:
    # 发送测试数据
    rs485.send_data("Pico RS485 Test")

    # 接收数据
    received = rs485.receive_data()
    # 如果接收到数据
    if received:
        # 处理接收到的数据
        rs485.process_received_data(received)

    # 延时1秒
    time.sleep(1)

<设备ID>:<数据内容>\r\n