php-modbus/examples/example_fc2.php

<?php

use PHPModbus\ModbusMaster;

$ip = filter_var($_GET['ip'], FILTER_VALIDATE_IP) ? $_GET['ip'] : '192.192.15.51';
$unitId = ((int)$_GET['unitid']) ?: 0;
$reference = ((int)$_GET['reference']) ?: 0;
$quantity = ((int)$_GET['quantity']) ?: 2;

$modbus = new ModbusMaster($ip, 'UDP');

try {
    // FC 2
    // read 2 input bits from address 0x0 (Wago input image)
    $recData = $modbus->readInputDiscretes($unitId, $reference, $quantity);
} catch (Exception $e) {
    // Print error information if any
    echo $modbus;
    echo $e;
    exit;
}

echo '<h1>Status</h1><pre>';
print_r($modbus);
echo '</pre>';
echo '<h1>Data</h1><pre>';
print_r($recData);
echo '</pre>';