'\" t
.\"     Title: modbus_read_registers
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: 10/18/2014
.\"    Manual: Libmodbus Manual
.\"    Source: libmodbus 3.0.6
.\"  Language: English
.\"
.TH "MODBUS_READ_REGISTER" "3" "10/18/2014" "libmodbus 3\&.0\&.6" "Libmodbus Manual"
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.SH "NAME"
modbus_read_registers \- read many registers
.SH "SYNOPSIS"
.sp
\fBint modbus_read_registers(modbus_t *\fR\fB\fIctx\fR\fR\fB, int \fR\fB\fIaddr\fR\fR\fB, int \fR\fB\fInb\fR\fR\fB, uint16_t *\fR\fB\fIdest\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fImodbus_read_registers()\fR function shall read the content of the \fInb\fR holding registers to the address \fIaddr\fR of the remote device\&. The result of reading is stored in \fIdest\fR array as word values (16 bits)\&.
.sp
You must take care to allocate enough memory to store the results in \fIdest\fR (at least \fInb\fR * sizeof(uint16_t))\&.
.sp
The function uses the Modbus function code 0x03 (read holding registers)\&.
.SH "RETURN VALUE"
.sp
The \fImodbus_read_registers()\fR function shall return the number of read registers if successful\&. Otherwise it shall return \-1 and set errno\&.
.SH "ERRORS"
.PP
EMBMDATA
.RS 4
Too many registers requested
.RE
.SH "EXAMPLE"
.sp
.if n \{\
.RS 4
.\}
.nf
modbus_t *ctx;
uint16_t tab_reg[64];
int rc;
int i;

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;
}

rc = modbus_read_registers(ctx, 0, 10, tab_reg);
if (rc == \-1) {
    fprintf(stderr, "%s\en", modbus_strerror(errno));
    return \-1;
}

for (i=0; i < rc; i++) {
    printf("reg[%d]=%d (0x%X)\en", i, tab_reg[i], tab_reg[i]);
}

modbus_close(ctx);
modbus_free(ctx);
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBmodbus_write_register\fR(3) \fBmodbus_write_registers\fR(3)
.SH "AUTHORS"
.sp
The libmodbus documentation was written by St\('ephane Raimbault <\m[blue]\fBstephane\&.raimbault@gmail\&.com\fR\m[]\&\s-2\u[1]\d\s+2>
.SH "NOTES"
.IP " 1." 4
stephane.raimbault@gmail.com
.RS 4
\%mailto:stephane.raimbault@gmail.com
.RE