// MODBUS protocol https://www.productinfo.schneider-electric.com/masterpactntnwcompactnsmodbuscommguide/masterpact-nt_nw_compact-ns-modbus-comm-guide/EN/BM_VEGA_MasterPact_IEC_2c93c0c3_T001013498.xml/$/TPC_Master_NS_MasterSlaveProtocol_2c93c0c3_T001013508

// ModbusMaster by Doc Walker in library
#include <ModbusMaster.h>        // Include ModbusMaster library for Modbus RTU

// RS485 control pins (STM32 example)
#define RS485_DE_PIN PB5   // DE (Driver Enable) pin
#define RS485_RE_PIN PA15  // RE (Receiver Enable) pin

// Create an instance of ModbusMaster for the master node
ModbusMaster node;

// Enable RS485 transceiver to send data (DE, RE pins)
void preTransmission() {
  digitalWrite(RS485_DE_PIN, HIGH);  // Enable transmit
  digitalWrite(RS485_RE_PIN, HIGH);  // Disable receive
}

// Enable RS485 transceiver to receive data
void postTransmission() {
  digitalWrite(RS485_DE_PIN, LOW);   // Disable transmit
  digitalWrite(RS485_RE_PIN, LOW);   // Enable receive
}

void setup() {
  // Initialize Serial2 for RS485 communication
  Serial2.begin(9600);

  // Set DE and RE pins as output
  pinMode(RS485_DE_PIN, OUTPUT);
  pinMode(RS485_RE_PIN, OUTPUT);
  postTransmission();  // Set to receive mode by default

  // Initialize Modbus communication with the slave node
  node.begin(1, Serial2);  // Set slave ID to 1, use Serial2 for communication

  // Assign the preTransmission and postTransmission callbacks
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);

  // Start Serial for debugging
  Serial.begin(9600);
  Serial.println("Modbus Master: Requesting Temperature from Slave");
}

void loop() {
  uint8_t result;
  uint16_t temperature;

  // Request holding register 0 from the slave node (where the temperature is stored)
  result = node.readHoldingRegisters(0, 1);  // Read 1 register starting from address 0

  // Check if the Modbus request was successful
  if (result == node.ku8MBSuccess) {
    // Read the temperature value from the response
    temperature = node.getResponseBuffer(0);  // Get the value from the first register (index 0)

    // Convert the value back to a floating-point temperature (assuming it's scaled by 100)
    float temperatureC = temperature / 100.0;

    // Print the temperature to the Serial Monitor
    Serial.print("Temperature from slave: ");
    Serial.print(temperatureC);
    Serial.println(" °C");
  } else {
    // Print error message if the Modbus request failed
    Serial.println("Failed to read from slave");
  }

  // Delay before next Modbus request
  delay(2000);  // Poll the slave every 2 seconds
}