Response not from requested slave

[f mariani]

Hi all,
this is my code:

#include <iostream>
#include <stdio.h>
#include "modbus.h"
#include <string.h>

//parameters for modbus_new_rtu
int  baud  = 9600;        //baud rate
char par   = 'O';        //parity
int  d_bit = 8;            //number of bits of data
int  s_bit = 1;            //bits of stop
int  slave = 2;

//parameters for modbus_read_registers
int index =    501;
int n_reg = 2;


using namespace std;

int main(){

    modbus_t *ctx;
    uint16_t tab_reg[64];
    uint32_t old_response_to_sec;
    uint32_t old_response_to_usec;
    uint32_t new_response_to_sec;
    uint32_t new_response_to_usec;
    int rc;

    ctx = modbus_new_rtu("COM2", baud, par, d_bit, s_bit);  //modbus_t *modbus_new_rtu(const char *device, int baud, char parity, int data_bit, int stop_bit);
    int s_stat = modbus_set_slave(ctx, slave);
    if (s_stat == -1) {
        fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
        modbus_free(ctx);
        return -1;
    }
    else
        cout << "Slave index: "<<slave<<endl;
   
    if (modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485) == -1)
        fprintf(stderr, "Unable to set mode: %s\n", modbus_strerror(errno));
   
    modbus_set_debug(ctx, TRUE);
    modbus_get_response_timeout(ctx, &old_response_to_sec, &old_response_to_usec);

    int c_stat = modbus_connect(ctx);
    if (c_stat == -1) {
        fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
        modbus_free(ctx);
        return -1;
    }
    else
        cout << "Connection started"<< endl;    

    modbus_get_response_timeout(ctx, &new_response_to_sec, &new_response_to_usec);
    if ((old_response_to_sec == new_response_to_sec) && (old_response_to_usec == new_response_to_usec)){
        cout << "No response timeout modification on connect"<<endl;
    }
    else{
        cout << "Response timeout modification on connect"<<endl;
        return -1;
    }
   
    rc = modbus_read_registers(ctx, index, n_reg, tab_reg);
    if (rc == -1){
        cout << "read failed: " << modbus_strerror(errno) << endl;
        return -1;
    }
    else {
        for (int i = 0; i<rc; i++){
            cout << "reg[" << i << "] = " << tab_reg[i] << endl;
        }
    }

    free(tab_reg);
    modbus_close(ctx);
    modbus_free(ctx);
    system("PAUSE");
    return 0;
}

when I run the program this is the error:

Slave index: 1
Unable to set mode: Unknown error

Opening COM2 at 9600 bauds (O, 8, 1)

Connection started
No response timeout modification on connect[01][03][01][F5][00][02][D5][C5]
Waiting for a confirmation...
<FD><FB><F7><FF><FD>
Request for slave 253 ignored (not 1)
The responding slave 253 isn't the requested slave 1
read failed: Response not from requested slave

My network is composed by my computer (master) and a plc Panasonic FP-X0. This error is shown only if I set the right address of the slave. If I don't set the right slaveID this is the error:

Slave index: 1
Unable to set mode: Unknown error
Opening COM2 at 9600 bauds (O, 8, 1)
Connection started
No response timeout modification on connect
[01][03][01][F5][00][02][D5][C5]
Waiting for a confirmation...
ERROR Unknown error: select
read failed: Unknown error

And the same happen when I try to write on a holding register.
Seem that something goes wrong with the response of PLC and not in the master trasmission.
Which could be the problem?
I found this discussion:
https://groups.google.com/forum/?hl=IT#!searchin/libmodbus/response$20not$20from$20requested/libmodbus/FgOkfWCLu-0/6LVc5e2gkoEJ
but the way followed buy this guys is no good for me because my code is the same of their corrected one.

I'm clueless. Somebody help me :(((.

Regards,
Federico.

[Eduardo Wirth]

Hello Mariani

you tried to use modbus_rtu_set_rts....

...

[Christophe Lemaire]

Hello,

I have the same problem to communicate with a electrical counter.

Do you have a solution ?