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