Unit RS485-ISO Arduino Tutorial

#include "M5Unified.h"
#include <Wire.h>
#include <ArduinoModbus.h>
#include <ArduinoRS485.h>

constexpr uint32_t MODBUS_BAUDRATE = 115200;
constexpr uint8_t SERVER_ID        = 0x01;
constexpr uint16_t REGISTER_ADDR   = 0x0000;

constexpr int PORT_A_RX_PIN = 1;
constexpr int PORT_A_TX_PIN = 2;
constexpr int PORT_C_RX_PIN = 18;
constexpr int PORT_C_TX_PIN = 17;

// PORT.A uses Serial2 as the Modbus RTU Client interface.
RS485Class RS485(Serial2, PORT_A_RX_PIN, PORT_A_TX_PIN, -1, -1);

// PORT.C uses Serial1 as the Modbus RTU Server interface.
RS485Class RS485PortC(Serial1, PORT_C_RX_PIN, PORT_C_TX_PIN, -1, -1);

ModbusRTUClientClass portAClient(RS485);
ModbusRTUServerClass portCServer(RS485PortC);

uint16_t transmitValue = 0;

void modbusServerTask(void *parameter);
void showResult(uint16_t sentValue, long receivedValue);
void haltWithError(const char *message);

void setup()
{
    M5.begin();
    Serial.begin(115200);
    delay(2000);

    M5.Display.setFont(&fonts::FreeMonoBold12pt7b);
    M5.Display.setTextColor(TFT_WHITE, TFT_BLACK);
    M5.Display.clear();
    M5.Display.println("RS485 initializing");

    // Release PORT.A from I2C before using its pins for Serial2.
    Wire.end();

    if (!portCServer.begin(SERVER_ID, MODBUS_BAUDRATE, SERIAL_8N1)) {
        haltWithError("Server init failed");
    }

    if (!portCServer.configureHoldingRegisters(REGISTER_ADDR, 1)) {
        haltWithError("Register init failed");
    }
    portCServer.holdingRegisterWrite(REGISTER_ADDR, 0);

    if (xTaskCreatePinnedToCore(modbusServerTask, "modbus-server", 4096,
                                nullptr, 2, nullptr, 0) != pdPASS) {
        haltWithError("Server task failed");
    }

    if (!portAClient.begin(MODBUS_BAUDRATE, SERIAL_8N1)) {
        haltWithError("Client init failed");
    }
    portAClient.setTimeout(500);

    Serial.println("PORT.A Client and PORT.C Server started");
    delay(100);
}

void loop()
{
    ++transmitValue;

    bool writeSuccess = portAClient.holdingRegisterWrite(
        SERVER_ID, REGISTER_ADDR, transmitValue);

    long receivedValue = -1;
    if (writeSuccess) {
        receivedValue = portAClient.holdingRegisterRead(
            SERVER_ID, REGISTER_ADDR);
    }

    showResult(transmitValue, receivedValue);
    delay(1000);
}

void modbusServerTask(void *parameter)
{
    while (true) {
        portCServer.poll();
        vTaskDelay(1);
    }
}

void showResult(uint16_t sentValue, long receivedValue)
{
    bool success = receivedValue >= 0 &&
                   static_cast<uint16_t>(receivedValue) == sentValue;

    Serial.printf("PORT.A TX: 0x%04X, PORT.C RX/TX: 0x%04lX, %s\n",
                  sentValue, receivedValue, success ? "PASS" : "FAIL");

    M5.Display.clear();
    M5.Display.setCursor(0, 0);
    M5.Display.println("Unit RS485-ISO Test");
    M5.Display.println("A Client -> C Server");
    M5.Display.printf("TX: 0x%04X\n", sentValue);

    if (receivedValue >= 0) {
        M5.Display.printf("RX: 0x%04lX\n", receivedValue);
    } else {
        M5.Display.println("RX: ERROR");
    }
    M5.Display.printf("Status: %s\n", success ? "PASS" : "FAIL");
}

void haltWithError(const char *message)
{
    Serial.println(message);
    M5.Display.clear();
    M5.Display.setCursor(0, 0);
    M5.Display.println(message);

    while (true) {
        delay(1000);
    }
}