modbus_new_rtu(3)

1MODBUS_NEW_RTU(3)              libmodbus Manual              MODBUS_NEW_RTU(3)
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NAME

6       modbus_new_rtu - create a libmodbus context for RTU
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SYNOPSIS

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

13       The modbus_new_rtu() function shall allocate and initialize a modbus_t
14       structure to communicate in RTU mode on a serial line.
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16       The device argument specifies the name of the serial port handled by
17       the OS, eg. "/dev/ttyS0" or "/dev/ttyUSB0". On Windows, it’s necessary
18       to prepend COM name with "\\.\" for COM number greater than 9, eg.
19       "\\\\.\\COM10". See
20       http://msdn.microsoft.com/en-us/library/aa365247(v=vs.85).aspx for
21       details
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23       The baud argument specifies the baud rate of the communication, eg.
24       9600, 19200, 57600, 115200, etc.
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26       The parity argument can have one of the following values
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28           •   N for none
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30           •   E for even
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32           •   O for odd
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34       The data_bits argument specifies the number of bits of data, the
35       allowed values are 5, 6, 7 and 8.
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37       The stop_bits argument specifies the bits of stop, the allowed values
38       are 1 and 2.
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40       Once the modbus_t structure is initialized, you must set the slave of
41       your device with modbus_set_slave(3) and connect to the serial bus with
42       modbus_connect(3).
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RETURN VALUE

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

50       EINVAL
51           An invalid argument was given.
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53       ENOMEM
54           Out of memory. Possibly, the application hits its memory limit
55           and/or whole system is running out of memory.
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EXAMPLE

58           modbus_t *ctx;
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60           ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);
61           if (ctx == NULL) {
62               fprintf(stderr, "Unable to create the libmodbus context\n");
63               return -1;
64           }
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66           modbus_set_slave(ctx, YOUR_DEVICE_ID);
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68           if (modbus_connect(ctx) == -1) {
69               fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
70               modbus_free(ctx);
71               return -1;
72           }
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AUTHORS

78       The libmodbus documentation was written by Stéphane Raimbault
79       <stephane.raimbault@gmail.com>
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83libmodbus v3.1.6                  02/04/2022                 MODBUS_NEW_RTU(3)