Arduino Modbus RTU VFD control

Question

I need help with this code:

/**
*  Modbus master example 1:
*  The purpose of this example is to query an array of data
*  from an external Modbus slave device.
*  The link media can be USB or RS232.
*
*  Recommended Modbus slave:
*  diagslave http://www.modbusdriver.com/diagslave.html
*
*  In a Linux box, run
*  "./diagslave /dev/ttyUSB0 -b 19200 -d 8 -s 1 -p none -m rtu -a 1"
* This is:
* serial port /dev/ttyUSB0 at 19200 baud 8N1
* RTU mode and address @1
*/

#include <ModbusRtu.h>

// data array for modbus network sharing
uint16_t au16data[16];
uint8_t u8state;

/**
*  Modbus object declaration
*  u8id : node id = 0 for master, = 1..247 for slave
*  u8serno : serial port (use 0 for Serial)
*  u8txenpin : 0 for RS-232 and USB-FTDI
*               or any pin number > 1 for RS-485
*/
Modbus master(0,0,2); // this is master and RS-232 or USB-FTDI, PIN 9 PARA INDICAR QUE TRASMITO

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

unsigned long u32wait;

void setup() {
 master.begin( 9600 ); // baud-rate at 19200
 master.setTimeOut( 2000 ); // if there is no answer in 2000 ms, roll over
 u32wait = millis() + 1000;
 u8state = 0;
}

void loop() {
 switch( u8state ) {
 case 0:
   if (millis() > u32wait) u8state++; // wait state
   break;
 case 1:
   telegram.u8id = 1; // slave address
   telegram.u8fct = 5; // function code (this one is registers read)
   telegram.u16RegAdd = 0; // start address in slave
   telegram.u16CoilsNo = 2; // number of elements (coils or registers) to read
   //telegram.au16reg = au16data; // pointer to a memory array in the Arduino

   // PARA EL VARIADOR OMRON MX1: MODBUS RTU 01 05 00 00 FF 00 -> START
   // 01 -> SLAVE (VFD OMRON)
   // 05 -> WRITE COIL
   //  00 00 -> ADDRESS COIL
   // FF 00 -> VALUES TO WRITE IN COIL FOR RUN

   telegram.au16reg[0] = 0;
   telegram.au16reg[1] = 0;
   telegram.au16reg[2] = 0;
   telegram.au16reg[3] = 0;
   telegram.au16reg[4] = 0;
   telegram.au16reg[5] = 0;
   telegram.au16reg[6] = 0;
   telegram.au16reg[7] = 0;

   telegram.au16reg[8] = 1;
   telegram.au16reg[9] = 1;
   telegram.au16reg[10] = 1;
   telegram.au16reg[11] = 1;
   telegram.au16reg[12] = 1;
   telegram.au16reg[13] = 1;
   telegram.au16reg[14] = 1;
   telegram.au16reg[15] = 1;


   master.query( telegram ); // send query (only once)
   delay(3500);

   telegram.u8id = 1; // slave address
   telegram.u8fct = 6; // function code (this one is registers read)
   telegram.u16RegAdd = 1; // start address in slave
   telegram.u16CoilsNo = 4; // number of elements (coils or registers) to read
   //telegram.au16reg = au16data; // pointer to a memory array in the Arduino
   //telegram.au16reg = 0000000111110100;

   // PARA EL VARIADOR OMRON MX1: MODBUS RTU 01 06 00 01 01 F4 -> CHANGE FQ
   // 01 -> SLAVE (VFD OMRON)
   // 06 -> WRITE IN REGISTE
   // 00 01 -> REGISTER ADDRESS
   // 01 F4 -> VALUE TO WRITE IN THE REGISTER TO CHANGE THE MOTOR FREQUENCY

   telegram.au16reg[0] = 0;
   telegram.au16reg[1] = 0;
   telegram.au16reg[2] = 0;
   telegram.au16reg[3] = 0;
   telegram.au16reg[4] = 0;
   telegram.au16reg[5] = 0;
   telegram.au16reg[6] = 0;
   telegram.au16reg[7] = 1;

   telegram.au16reg[8] = 1;
   telegram.au16reg[9] = 1;
   telegram.au16reg[10] = 1;
   telegram.au16reg[11] = 1;
   telegram.au16reg[12] = 0;
   telegram.au16reg[13] = 1;
   telegram.au16reg[14] = 0;
   telegram.au16reg[15] = 0;

   master.query( telegram ); // send query (only once)
   delay(3500);
   telegram.u8id = 1; // slave address
   telegram.u8fct = 5; // function code (this one is registers read)
   telegram.u16RegAdd = 1; // start address in slave
   telegram.u16CoilsNo = 2; // number of elements (coils or registers) to read
   //telegram.au16reg = au16data; // pointer to a memory array in the Arduino

   // PARA EL VARIADOR OMRON MX1: MODBUS RTU 01 05 00 00 00 00 -> STOP
   // 01 -> ESCLAVO (VARIADOR OMRON)
   // 05 -> ESCRIBIR EN UNA BOBINA
   // 00 00 -> DIRECCION DE LA BOBINA
   // 00 00 -> VALOR A ESCRIBIR EN LA BOBINA PARA STOP

   telegram.au16reg[0] = 0;
   telegram.au16reg[1] = 0;
   telegram.au16reg[2] = 0;
   telegram.au16reg[3] = 0;
   telegram.au16reg[4] = 0;
   telegram.au16reg[5] = 0;
   telegram.au16reg[6] = 0;
   telegram.au16reg[7] = 0;
   telegram.au16reg[8] = 0;
   telegram.au16reg[9] = 0;
   telegram.au16reg[10] = 0;
   telegram.au16reg[11] = 0;
   telegram.au16reg[12] = 0;
   telegram.au16reg[13] = 0;
   telegram.au16reg[14] = 0;
   telegram.au16reg[15] = 0;
   master.query( telegram ); // send query (only once)
   delay(3500);
   u8state++;
   break;
 case 2:
   master.poll(); // check incoming messages
   if (master.getState() == COM_IDLE) {
     u8state = 0;
     u32wait = millis() + 100;
   }
   break;
 }
}

I've managed to send RUN command to VFD but i can't (so far) send the change frequency command "01 06 00 01 01 F4" + CRC check.

When I connect logic analyzer with modbus rtu decoder, it shows "Device ID:'1' Function Write single coil ('5') Addr: '0' value: '65280' Chksum: '14988'.

The problem is that it pass only 1 telegram (array of packets) for command "RUN" but no the two others. Any help will be appreciated.

This is the link for VFD Omron MX: https://industrial.omron.us/en/media/I570-E2-02B_3G3MX2_UsersManual_tcm849-112721.pdf

TIA

Answer 1

You should update the comments and remove unused settings like the count fields for request with one value (function 5 and 6).

au16reg are the data to be send. ignore the binary format from the example.

To send a value of the coil or register set the value to telegram.au16reg[0].

For the Modbus message protocol see for example the Wikipedia article.