1MODBUS_SEND_RAW_REQU(3)        libmodbus Manual        MODBUS_SEND_RAW_REQU(3)
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NAME

6       modbus_send_raw_request - send a raw request
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SYNOPSIS

9       int modbus_send_raw_request(modbus_t *ctx, const uint8_t *raw_req, int
10       raw_req_length);
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DESCRIPTION

13       The modbus_send_raw_request() function shall send a request via the
14       socket of the context ctx. This function must be used for debugging
15       purposes because you have to take care to make a valid request by hand.
16       The function only adds to the message, the header or CRC of the
17       selected backend, so raw_req must start and contain at least a
18       slave/unit identifier and a function code. This function can be used to
19       send request not handled by the library.
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21       The public header of libmodbus provides a list of supported Modbus
22       functions codes, prefixed by MODBUS_FC_ (eg.
23       MODBUS_FC_READ_HOLDING_REGISTERS), to help build of raw requests.
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RETURN VALUE

26       The function shall return the full message length, counting the extra
27       data relating to the backend, if successful. Otherwise it shall return
28       -1 and set errno.
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EXAMPLE

31           modbus_t *ctx;
32           /* Read 5 holding registers from address 1 */
33           uint8_t raw_req[] = { 0xFF, MODBUS_FC_READ_HOLDING_REGISTERS, 0x00, 0x01, 0x0, 0x05 };
34           int req_length;
35           uint8_t rsp[MODBUS_TCP_MAX_ADU_LENGTH];
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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           req_length = modbus_send_raw_request(ctx, raw_req, 6 * sizeof(uint8_t));
45           modbus_receive_confirmation(ctx, rsp);
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47           modbus_close(ctx);
48           modbus_free(ctx);
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SEE ALSO

51       modbus_receive_confirmation(3)
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AUTHORS

54       The libmodbus documentation was written by Stéphane Raimbault
55       <stephane.raimbault@gmail.com>
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59libmodbus v3.1.6                  02/04/2022           MODBUS_SEND_RAW_REQU(3)
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