Thinking of getting started

Hi Derrick, I have implemented Modbus by using https://github.com/smarmengol/Modbus-Master-Slave-for-Arduino on the Industruino (as Master) and an Arduino Uno (as Slave). In order to get it to run on the Industruino, I had to modify the code - replacing Serial with Serial1, and ensuring that I set the Tx_En_Pin to 9. In order to get it running on the Uno I had to modify the code to use Software Serial.

So:

#include <ModbusRtu.h> // mondified to have port 0 point to Serial1

// Modbus

uint16_t au16data[16]; //!< data array for modbus network sharing
uint8_t u8state; //!< machine state
uint8_t u8query; //!< pointer to message query
unsigned long u32wait;

Modbus master(0,1,9); // this is master on Serial1, with TX_EN on Pin 9 for RS-485

// Timer driving reading / sending of messages
Timer modbusTimer;

/**
 * This is an structe which contains a query to a slave device
 */
modbus_t telegram[1];

void setup() {

// Modbus
  #define TOTAL_TELEGRAMS 2
  // telegram 0: read registers from Slave 1
  telegram[0].u8id = 1; // slave address
  telegram[0].u8fct = 3; // function code (this one is registers read)
  telegram[0].u16RegAdd = 0; // start address in slave
  telegram[0].u16CoilsNo = 4; // number of elements (coils or registers) to read
  telegram[0].au16reg = au16data; // pointer to a memory array in the Arduino

  // telegram 1: read registers from Slave 2
  telegram[1].u8id = 2; // slave address
  telegram[1].u8fct = 3; // function code (this one is write a single register)
  telegram[1].u16RegAdd = 0; // start address in slave
  telegram[1].u16CoilsNo = 3; // number of elements (coils or registers) to read
  telegram[1].au16reg = au16data+4; // pointer to a memory array in the Arduino

 

  master.begin(9600); // baud-rate at 9600
  master.setTimeOut(2000); // if there is no answer in 5000 ms, roll over
  u32wait = millis() + 1000;
  u8state = u8query = 0;
  int modbusEvent = modbusTimer.every(500, getModbusData);  // Every 500mSec

}

void loop() {

  // Handle modbus timer
  modbusTimer.update();

}

void getModbusData()
{
  switch( u8state ) {
    case 0:
      master.query( telegram[0] );
      master.query( telegram[1] );
      //master.query( telegram[u8query] ); // send query (only once)
      u8state++;
      u8query++;
      if (u8query > TOTAL_TELEGRAMS) u8query = 0;
      break;
    case 1:
      master.poll(); // check incoming messages
      if (master.getState() == COM_IDLE) {
        u8state = 0;
      }
      break;
  }
}

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Mark Leyden

Mark Leyden

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Answered on 8/31/15, 9:22 PM

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