modbus_mapping_new_start_address(3)

1MODBUS_MAPPING_NEW_S(3)        libmodbus Manual        MODBUS_MAPPING_NEW_S(3)
2
3
4

NAME

6       modbus_mapping_new_start_address - allocate four arrays of bits and
7       registers accessible from their starting addresses
8

SYNOPSIS

10       modbus_mapping_t modbus_mapping_new_start_address(int start_bits, int
11       nb_bits, int start_input_bits, int nb_input_bits, int start_registers,
12       int nb_registers, int start_input_registers, int nb_input_registers);*
13

DESCRIPTION

15       The modbus_mapping_new_start_address() function shall allocate four
16       arrays to store bits, input bits, registers and inputs registers. The
17       pointers are stored in modbus_mapping_t structure. All values of the
18       arrays are initialized to zero.
19
20       The different starting adresses make it possible to place the mapping
21       at any address in each address space. This way, you can give access to
22       values stored at high adresses without allocating memory from the
23       address zero, for eg. to make available registers from 10000 to 10009,
24       you can use:
25
26           mb_mapping = modbus_mapping_new_start_address(0, 0, 0, 0, 10000, 10, 0, 0);
27
28       With this code, only 10 registers (uint16_t) are allocated.
29
30       If it isn’t necessary to allocate an array for a specific type of data,
31       you can pass the zero value in argument, the associated pointer will be
32       NULL.
33
34       This function is convenient to handle requests in a Modbus
35       server/slave.
36

RETURN VALUE

38       The modbus_mapping_new_start_address() function shall return the new
39       allocated structure if successful. Otherwise it shall return NULL and
40       set errno.
41

ERRORS

43       ENOMEM
44           Not enough memory
45

EXAMPLE

47           /* The first value of each array is accessible at the defined address.
48              The end address is ADDRESS + NB - 1. */
49           mb_mapping = modbus_mapping_new_start_address(BITS_ADDRESS, BITS_NB,
50                                           INPUT_BITS_ADDRESS, INPUT_BITS_NB,
51                                           REGISTERS_ADDRESS, REGISTERS_NB,
52                                           INPUT_REGISTERS_ADDRESS, INPUT_REGISTERS_NB);
53           if (mb_mapping == NULL) {
54               fprintf(stderr, "Failed to allocate the mapping: %s\n",
55                       modbus_strerror(errno));
56               modbus_free(ctx);
57               return -1;
58           }
59

AUTHORS

64       The libmodbus documentation was written by Stéphane Raimbault
65       <stephane.raimbault@gmail.com>
66
67
68
69libmodbus v3.1.6                  01/19/2023           MODBUS_MAPPING_NEW_S(3)