NAME

       modbus_new_rtu - create a libmodbus context for RTU

SYNOPSIS

       modbus_t *modbus_new_rtu(const char *device, int baud, char parity, int data_bit, int
       stop_bit);

DESCRIPTION

       The modbus_new_rtu() function shall allocate and initialize a modbus_t structure to
       communicate in RTU mode on a serial line.

       The device argument specifies the name of the serial port handled by the OS, eg.
       "/dev/ttyS0" or "/dev/ttyUSB0". On Windows, it’s necessary to prepend COM name with "\\.\"
       for COM number greater than 9, eg. "\\\\.\\COM10". See
       http://msdn.microsoft.com/en-us/library/aa365247(v=vs.85).aspx for details

       The baud argument specifies the baud rate of the communication, eg. 9600, 19200, 57600,
       115200, etc.

       The parity argument can have one of the following values

           •   N for none

           •   E for even

           •   O for odd

       The data_bits argument specifies the number of bits of data, the allowed values are 5, 6,
       7 and 8.

       The stop_bits argument specifies the bits of stop, the allowed values are 1 and 2.

       Once the modbus_t structure is initialized, you must set the slave of your device with
       modbus_set_slave(3) and connect to the serial bus with modbus_connect(3).

RETURN VALUE

       The function shall return a pointer to a modbus_t structure if successful. Otherwise it
       shall return NULL and set errno to one of the values defined below.

ERRORS

       EINVAL
           An invalid argument was given.

       ENOMEM
           Out of memory. Possibly, the application hits its memory limit and/or whole system is
           running out of memory.

EXAMPLE

           modbus_t *ctx;

           ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);
           if (ctx == NULL) {
               fprintf(stderr, "Unable to create the libmodbus context\n");
               return -1;
           }

           modbus_set_slave(ctx, YOUR_DEVICE_ID);

           if (modbus_connect(ctx) == -1) {
               fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
               modbus_free(ctx);
               return -1;
           }

SEE ALSO

       modbus_new_tcp(3) modbus_free(3)

AUTHORS

       The libmodbus documentation was written by Stéphane Raimbault
       <stephane.raimbault@gmail.com>