Basic UNO sketch reading MAX31865 v2

modbus_MAX31865.ino

//-----------------------------------------------------------------------------
// Copyright 2018 Thiago Alves
// This file is part of the OpenPLC Software Stack.
//
// OpenPLC is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// OpenPLC is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with OpenPLC.  If not, see <http://www.gnu.org/licenses/>.
//------
//
// This is the main file for the OpenPLC Arduino firmware. It contains the a
// Modbus RTU library to communciate with OpenPLC host as a slave device.
//
// Thiago Alves, Aug 2018
//-----------------------------------------------------------------------------
#define USE_HOLDING_REGISTERS_ONLY    //  you only need holding registers... this save sketch space. 
#include <Arduino.h>
#include "Modbus.h"
#include "ModbusSerial.h"
#include <Adafruit_MAX31865.h>

//ModBus Port information
#define BAUD        115200
#define ID          0
#define TXPIN       -1

//Modbus Object
ModbusSerial modbus;

// Use software SPI: CS, DI, DO, CLK
//Adafruit_MAX31865 temp1 = Adafruit_MAX31865(10, 11, 12, 13);
// use hardware SPI, just pass in the CS pin
Adafruit_MAX31865 temp1 = Adafruit_MAX31865(10);  //  can attach multiple devices with different CS pins

// The value of the Rref resistor. Use 430.0 for PT100 and 4300.0 for PT1000
#define RREF      430.0
// The 'nominal' 0-degrees-C resistance of the sensor
// 100.0 for PT100, 1000.0 for PT1000
#define RNOMINAL  100.0

void setup()
{
      
    //Config Modbus Serial (port, speed, rs485 tx pin)
    modbus.config(&Serial, BAUD, -1);
    
    //Set the Slave ID
    modbus.setSlaveId(ID); 
    
     modbus.addIreg(0, 0); //  temp register and set to 0 
     modbus.addIreg(1, 0 ); // error register 

     
     temp1.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary

}

uint32_t timer = 0; 

void loop()
{
    //Run the main modbus task
    modbus.task();

    if (millis() - timer > 1000) //  reads data once per second 
    {
      uint16_t rtd = temp1.readRTD(); //  read the value...  luckily the result returned is 16bit.. 
      uint8_t fault = temp1.readFault();
      // the rest of the conversion can be done in OCD as a fixed formula!  
      if (!fault) {
        modbus.Ireg(0, rtd); //  this sets holding register 0 to the read value;; 
        modbus.Ireg(1,0);  // clear error if one 
      } else {
        modbus.Ireg(1,fault);  //  allow sending of fault back to openplc... 
        temp1.clearFault();
      }
      timer = millis(); 
    }

/*  Don't use delay() in main loop as it will stop modbus.task() from runninig  */ 
    

}