if (argc != 4 && argc != 5)
{
    printf("Error: Invalid arguments.\n\n");    
    usage(argv[0]);
}

host    = argv[1];
command = argv[2];

if (strcmp(command, "write") == 0)
{
    if (argc != 5)
    {
       printf("Error: Invalid arguments: COMMAND write requies additional argument VALUE\n\n");    
       usage(argv[0]);        
    }

    addr  = atoi(argv[3]);
    value = atoi(argv[4]);    
}
else if (strcmp(command, "read") == 0)
{
    addr = atoi(argv[3]);    
}
else if (strcmp(command, "readrange") == 0)
{
    addr = atoi(argv[3]);
    range = 8;
}    
else
{
    printf("Error: Invalid COMMAND: %s\n\n", command);
    usage(argv[0]);
}

  modbus_read_coil_status(pkt, addr, range);

// setup tcp
if (modbus_tcp_init(host, port, &handle) != 0)
{
    printf("%s: modbus_tcp_init failed: %s.\n", __PRETTY_FUNCTION__, modbus_error_str);
    return 0;
}

if (debug)
    modbus_frame_print(pkt);

// Send command
if (modbus_tcp_send(&handle, pkt) != 0)
{
    printf("%s: modbus_tcp_send failed: %s.\n", __PRETTY_FUNCTION__, modbus_error_str);
    return 0;       
}

// recv response
if (modbus_tcp_recv(&handle, pkt) != 0)
{
    printf("%s: modbus_tcp_recv failed: %s.\n", __PRETTY_FUNCTION__, modbus_error_str);
    return 0;       
}

if (modbus_frame_verify(pkt) == -1)
{
    printf("%s: modbus_frame_verify failed: %s\n", __PRETTY_FUNCTION__, modbus_error_str);
    return 0;               
}

if (debug)
    modbus_frame_print(pkt);

if (strcmp(command, "write") == 0)
{
    ; //    
}
else // a read command
{
    for (i = range - 1; i >= 0; i--)
    {
        printf("%d ", pkt->data_buff[1] & (0x01<<i) ? 1 : 0);
    }
    printf("\n");
}
modbus_frame_free(pkt);