'\" t
.\"     Title: modbus_send_raw_request
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 10/15/2022
.\"    Manual: libmodbus Manual
.\"    Source: libmodbus v3.1.6
.\"  Language: English
.\"
.TH "MODBUS_SEND_RAW_REQU" "3" "10/15/2022" "libmodbus v3\&.1\&.6" "libmodbus Manual"
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.SH "NAME"
modbus_send_raw_request \- send a raw request
.SH "SYNOPSIS"
.sp
\fBint modbus_send_raw_request(modbus_t *\fR\fB\fIctx\fR\fR\fB, const uint8_t *\fR\fB\fIraw_req\fR\fR\fB, int \fR\fB\fIraw_req_length\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fBmodbus_send_raw_request()\fR function shall send a request via the socket of the context \fIctx\fR\&. This function must be used for debugging purposes because you have to take care to make a valid request by hand\&. The function only adds to the message, the header or CRC of the selected backend, so \fIraw_req\fR must start and contain at least a slave/unit identifier and a function code\&. This function can be used to send request not handled by the library\&.
.sp
The public header of libmodbus provides a list of supported Modbus functions codes, prefixed by MODBUS_FC_ (eg\&. MODBUS_FC_READ_HOLDING_REGISTERS), to help build of raw requests\&.
.SH "RETURN VALUE"
.sp
The function shall return the full message length, counting the extra data relating to the backend, if successful\&. Otherwise it shall return \-1 and set errno\&.
.SH "EXAMPLE"
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.if n \{\
.RS 4
.\}
.nf
modbus_t *ctx;
/* Read 5 holding registers from address 1 */
uint8_t raw_req[] = { 0xFF, MODBUS_FC_READ_HOLDING_REGISTERS, 0x00, 0x01, 0x0, 0x05 };
int req_length;
uint8_t rsp[MODBUS_TCP_MAX_ADU_LENGTH];

ctx = modbus_new_tcp("127\&.0\&.0\&.1", 1502);
if (modbus_connect(ctx) == \-1) {
    fprintf(stderr, "Connection failed: %s\en", modbus_strerror(errno));
    modbus_free(ctx);
    return \-1;
}

req_length = modbus_send_raw_request(ctx, raw_req, 6 * sizeof(uint8_t));
modbus_receive_confirmation(ctx, rsp);

modbus_close(ctx);
modbus_free(ctx);
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBmodbus_receive_confirmation\fR(3)
.SH "AUTHORS"
.sp
The libmodbus documentation was written by Stéphane Raimbault <stephane\&.raimbault@gmail\&.com>