5 years, 2 months ago.

Any code for Modbus master?

Is there any implementation of Modbus master? because I found https://developer.mbed.org/users/cam/code/Modbus/ but only work as slave.

Are you trying MODBUS over TCP/IP or MODBUS over RS-485?

posted by Neel Shah 13 Dec 2015

Hello. A simple gift for you. Just tips... Complete rest by yourself..

#include "mbed.h"

RawSerial modbus(PB_6, PA_10);
DigitalOut modbus_transmit(PC_0, 0);
Serial pc(USBTX, USBRX);

volatile char modbus_buffer_char;
uint8_t                modbus_input_buffer[12];
volatile uint8_t    modbus_input_buffer_counter = 0;
volatile bool       modbus_interrupt_complete = false;

uint32_t modbus_result;
char datam[8] = {0x01,0x03,0x00,0x00,0x00,0x02,0xC4,0x0B};
char datam2[8] = {0x01,0x03, 0x80,0x0A, 0x00, 0x01, 0x8D, 0xC8} ;


uint16_t modbus_crc(uint8_t* buf, int len)
{
    uint16_t crc = 0xFFFF;

    for (int pos = 0; pos < len; pos++) {
        crc ^= (uint16_t)buf[pos];          // XOR byte into least sig. byte of crc

        for (int i = 8; i != 0; i--) {    // Loop over each bit
            if ((crc & 0x0001) != 0) {      // If the LSB is set
                crc >>= 1;                    // Shift right and XOR 0xA001
                crc ^= 0xA001;
            } else                          // Else LSB is not set
                crc >>= 1;                    // Just shift right
        }
    }
    // Note, this number has low and high bytes swapped, so use it accordingly (or swap bytes)
    return crc;
}

/*  ISR for MODBUS  */
void modbus_rx_isr()
{
    if (modbus.readable()) {
        modbus_buffer_char = modbus.getc();
        if (modbus_input_buffer_counter == 0 && modbus_buffer_char == 0x00) {
            modbus_input_buffer_counter = 0;
        } else {
            modbus_input_buffer[modbus_input_buffer_counter] = modbus_buffer_char;
            modbus_input_buffer_counter++;
        }
    }

    if (modbus_input_buffer_counter > modbus_input_buffer[2] + 4) {
        modbus_interrupt_complete = true;
        modbus_input_buffer_counter = 0;
    }
}

void modbus_read_L1V(uint8_t slave_address)
{
    uint8_t L1V[8] = {slave_address, 0x03, 0x00, 0x06, 0x00, 0x02, 0x00, 0x00};

    L1V[6] = modbus_crc(L1V,6) & 0xFF;
    L1V[7] = (modbus_crc(L1V,6)>>8) & 0xFF;

    modbus_transmit = 1;
    //wait_ms(5);


    for (uint8_t i = 0; i < 8; i++) {
        modbus.putc(L1V[i]);
    }


    //modbus.putc(crc_hi);
    //modbus.putc(crc_low);




    wait_ms(5);
    modbus_transmit = 0;


}


posted by Kamil M 21 Dec 2015

...and main

int main()
{
    modbus.baud(9600);
    printf("start\n\r");
    modbus.attach(&modbus_rx_isr, Serial::RxIrq);
    //modbus_transmit = 1;

    while(1) {

        modbus_read_L1V(0x01);


        if (modbus_interrupt_complete) {

            modbus_input_buffer_counter = 0;
            modbus_interrupt_complete = false;



            if (modbus_input_buffer[2] == 2) {
                uint16_t l1v1;
                l1v1 = (modbus_input_buffer[3] << 8) | modbus_input_buffer[4];
                memset (modbus_input_buffer, 0, sizeof(modbus_input_buffer));
                //printf("start\n\r");
                printf("\r\n%.1f\r\n", l1v1*0.001);
                l1v1=0;

            } else if (modbus_input_buffer[2] == 4) {
                uint32_t l1v2;
                l1v2 = (modbus_input_buffer[3] << 24) | (modbus_input_buffer[4] << 16) | (modbus_input_buffer[5] << 8) | modbus_input_buffer[6];
                memset (modbus_input_buffer, 0, sizeof(modbus_input_buffer));
                //printf("start\n\r");
                printf("%.1f\n\r", l1v2*0.001);
                l1v2=0;
            }
        }

        wait(1);
    }
}

posted by Kamil M 21 Dec 2015

This is for MODBUS-RS485 i.e. RTU :)

posted by Kamil M 21 Dec 2015

can u please help me for modbus slave?

posted by somesh burkule 03 Apr 2018

2 Answers

5 years, 2 months ago.

Are you trying MODBUS over TCP/IP or MODBUS over RS-485?

Accepted Answer

over RS-232 and Modbus RTU

posted by Miguel Alarcón Ortiz 13 Dec 2015
5 years, 2 months ago.

You can try FreeModbus - http://sourceforge.net/projects/freemodbus.berlios/files/?source=navbar

thank for reply. you can see this link in a implementation on mbed about freemodbus https://developer.mbed.org/users/cam/code/Modbus/ but the implementation only works like slave if you check state machine you will see it. But my goal mbed works like master I mean mbed will send the request and will wait to reponse.

posted by Miguel Alarcón Ortiz 13 Dec 2015

It's not difficult to modify Freemodbus to handle master functionality.

You can also go for https://code.google.com/p/simple-modbus/ , which provides limited master functionality out of the box.

posted by Honza T. 13 Dec 2015