ERROR connection timeout (RS485)

[Andrey Strunin]

I try to use libmodbus with RS485
I have problem...
Master must send right modbus packet, but i see timeout error alltime

My code:

    struct timeval response_timeout;
    response_timeout.tv_sec = 0;
    response_timeout.tv_usec = 99999;
    uint16_t tab_reg[32]={0};
    modbus_t* ctx = modbus_new_rtu("/dev/serusb2", 115200, 'N', 8, 2);
    if (ctx==NULL)std::cout<<"Unable init modbus context \n";
    modbus_set_slave(ctx,0x0B);
    modbus_connect(ctx);
    modbus_set_response_timeout(ctx,&response_timeout);
    modbus_set_debug(ctx, TRUE);
    modbus_read_registers(ctx, 0, 5, tab_reg);
    for(int i=0;i<5;i++)
    {
        printf(" %d",tab_reg[i]);
    }
    modbus_flush(ctx);
    modbus_close(ctx);
    modbus_free(ctx);

Debug info:

[0B][03][00][00][00][05][85][63]
Waiting for a confirmation...(Timeout is very long. The slave responds, and only then the program goes on. )
ERROR Connection timed out: select
<0B><03><10><10><01><10><01><10><01><10><01><10><01><F2><3D> 0 0 0 0 00 bytes flushed


<0B><03><10><10><01><10><01><10><01><10><01><10><01><F2><3D>  - it's right packet...

[giorgio foga]

Hy I have the same result ..... every 10'' at the start of my pc ..... 30min after everything is resolved and working properly. You've solved somehow?

[Jesse Stone]

i meet this problem too.
i test one side is ubuntu 14.4 PC unit-test-client another side is android dev board. unit-test-server

in client
    rc = modbus_write_bit(ctx, UT_BITS_ADDRESS, ON);
    printf("1/2 modbus_write_bit: ");
    ASSERT_TRUE(rc == 1, "");
    rc = modbus_write_bit(ctx, UT_BITS_ADDRESS, ON); //add this to test

in server
  do {
            rc = modbus_receive(ctx, query);
            /* Filtered queries return 0 */
        } while (rc == 0);

then server only receive once...


finally i change hardware and use the usb to rs485 serial on both side
Bus 003 Device 010: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter
test all pass



giorgio foga於 2013年10月4日星期五 UTC+8下午8時11分16秒寫道：