libmodbus/doc/modbus_read_registers.txt

modbus_read_registers(3)
========================


NAME
----
modbus_read_registers - read many registers


SYNOPSIS
--------
*int modbus_read_registers(modbus_t *'ctx', int 'addr', int 'nb', uint16_t *'dest');*


DESCRIPTION
-----------
The *modbus_read_registers()* function shall read the content of the _nb_
holding registers to the address _addr_ of the remote device. The result of
reading is stored in _dest_ array as word values (16 bits).

You must take care to allocate enough memory to store the results in _dest_
(at least _nb_ * sizeof(uint16_t)).

The function uses the Modbus function code 0x03 (read holding registers).


RETURN VALUE
------------
The function shall return the number of read registers
if successful. Otherwise it shall return -1 and set errno.


ERRORS
------
*EMBMDATA*::
Too many registers requested


EXAMPLE
-------
[source,c]
-------------------
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\n", modbus_strerror(errno));
    modbus_free(ctx);
    return -1;
}

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

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

modbus_close(ctx);
modbus_free(ctx);
-------------------


SEE ALSO
--------
linkmb:modbus_write_register[3]
linkmb:modbus_write_registers[3]


AUTHORS
-------
The libmodbus documentation was written by Stéphane Raimbault
<stephane.raimbault@gmail.com>