Documentation

// MAX485 RS-485 - Arduino Example (sender + listener)
// RO->D10, DI->D11, RE+DE->D3, VCC->5V

#include <SoftwareSerial.h>

const int DIR_PIN = 3;                  // HIGH = TX, LOW = RX
SoftwareSerial rs485(10, 11);           // RX, TX
unsigned long counter = 0;

void setTransmit(bool tx) {
  digitalWrite(DIR_PIN, tx ? HIGH : LOW);
  delayMicroseconds(50);                // let the driver settle
}

void setup() {
  Serial.begin(115200);
  rs485.begin(9600);
  pinMode(DIR_PIN, OUTPUT);
  setTransmit(false);
  Serial.println("RS-485 node ready");
}

void loop() {
  // --- send one message ---
  setTransmit(true);
  rs485.print("MSG ");
  rs485.println(counter++);
  rs485.flush();                        // wait until fully shifted out
  setTransmit(false);

  // --- listen for replies for 1 second ---
  unsigned long t0 = millis();
  while (millis() - t0 < 1000) {
    if (rs485.available()) {
      String line = rs485.readStringUntil('\n');
      Serial.print("Received: ");
      Serial.println(line);
    }
  }
}

// MAX485 RS-485 - ESP32 Example (hardware UART2)
// RO->GPIO16, DI->GPIO17, RE+DE->GPIO4

const int DIR_PIN = 4;
unsigned long counter = 0;

void setTransmit(bool tx) {
  digitalWrite(DIR_PIN, tx ? HIGH : LOW);
  delayMicroseconds(50);
}

void setup() {
  Serial.begin(115200);
  Serial2.begin(9600, SERIAL_8N1, 16, 17);   // RX=16, TX=17
  pinMode(DIR_PIN, OUTPUT);
  setTransmit(false);
  Serial.println("RS-485 node ready");
}

void loop() {
  setTransmit(true);
  Serial2.printf("ESP32 MSG %lu\n", counter++);
  Serial2.flush();
  setTransmit(false);

  unsigned long t0 = millis();
  while (millis() - t0 < 1000) {
    if (Serial2.available()) {
      String line = Serial2.readStringUntil('\n');
      Serial.print("Received: ");
      Serial.println(line);
    }
  }
}

#!/usr/bin/env python3
# MAX485 RS-485 - Raspberry Pi Example
# RO->GPIO15(RXD), DI->GPIO14(TXD), RE+DE->GPIO17
# Install: pip3 install pyserial ; enable UART in raspi-config

import serial
import time
import RPi.GPIO as GPIO

DIR_PIN = 17
GPIO.setmode(GPIO.BCM)
GPIO.setup(DIR_PIN, GPIO.OUT, initial=GPIO.LOW)

port = serial.Serial("/dev/serial0", 9600, timeout=0.2)

def send(msg):
    GPIO.output(DIR_PIN, GPIO.HIGH)
    time.sleep(0.0001)
    port.write((msg + "\n").encode())
    port.flush()
    time.sleep(0.002)                 # drain the UART FIFO
    GPIO.output(DIR_PIN, GPIO.LOW)

counter = 0
print("RS-485 node ready")
try:
    while True:
        send("PI MSG {}".format(counter))
        counter += 1

        t0 = time.time()
        while time.time() - t0 < 1.0:
            line = port.readline()
            if line:
                print("Received:", line.decode(errors="ignore").strip())
except KeyboardInterrupt:
    GPIO.cleanup()
    print("Stopped by user")

# MAX485 RS-485 - Pico MicroPython Example
# RO->GP1, DI->GP0, RE+DE->GP2

from machine import UART, Pin
import time

uart = UART(0, baudrate=9600, tx=Pin(0), rx=Pin(1))
dir_pin = Pin(2, Pin.OUT, value=0)     # 0 = receive

def send(msg):
    dir_pin.value(1)
    time.sleep_us(100)
    uart.write(msg + "\n")
    # wait for the frame to leave the shift register
    time.sleep_ms(2 + len(msg))
    dir_pin.value(0)

counter = 0
print("RS-485 node ready")
while True:
    send("PICO MSG {}".format(counter))
    counter += 1

    t0 = time.ticks_ms()
    while time.ticks_diff(time.ticks_ms(), t0) < 1000:
        if uart.any():
            line = uart.readline()
            if line:
                print("Received:", line.decode().strip())