modbus_read_registers(3)

1MODBUS_READ_REGISTER(3)        Libmodbus Manual        MODBUS_READ_REGISTER(3)
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NAME

6       modbus_read_registers - read many registers
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SYNOPSIS

9       int modbus_read_registers(modbus_t *ctx, int addr, int nb, uint16_t
10       *dest);
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DESCRIPTION

13       The modbus_read_registers() function shall read the content of the nb
14       holding registers to the address addr of the remote device. The result
15       of reading is stored in dest array as word values (16 bits).
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17       You must take care to allocate enough memory to store the results in
18       dest (at least nb * sizeof(uint16_t)).
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20       The function uses the Modbus function code 0x03 (read holding
21       registers).
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RETURN VALUE

24       The modbus_read_registers() function shall return the number of read
25       registers if successful. Otherwise it shall return -1 and set errno.
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ERRORS

28       EMBMDATA
29           Too many registers requested
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EXAMPLE

32           modbus_t *ctx;
33           uint16_t tab_reg[64];
34           int rc;
35           int i;
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37           ctx = modbus_new_tcp("127.0.0.1", 1502);
38           if (modbus_connect(ctx) == -1) {
39               fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
40               modbus_free(ctx);
41               return -1;
42           }
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44           rc = modbus_read_registers(ctx, 0, 10, tab_reg);
45           if (rc == -1) {
46               fprintf(stderr, "%s\n", modbus_strerror(errno));
47               return -1;
48           }
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50           for (i=0; i < rc; i++) {
51               printf("reg[%d]=%d (0x%X)\n", i, tab_reg[i], tab_reg[i]);
52           }
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54           modbus_close(ctx);
55           modbus_free(ctx);
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AUTHORS

61       The libmodbus documentation was written by Stéphane Raimbault
62       <stephane.raimbault@gmail.com[1]>
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NOTES

65        1. stephane.raimbault@gmail.com
66           mailto:stephane.raimbault@gmail.com
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70libmodbus 3.0.8                   07/31/2019           MODBUS_READ_REGISTER(3)