$fc3 = ReadRegistersBuilder::newReadHoldingRegisters('tcp://127.0.0.1:5022')
    ->bit(256, 15, 'pump2_feedbackalarm_do')
    // will be split into 2 requests as 1 request can return only range of 124 registers max
    ->int16(657, 'battery3_voltage_wo')
    // will be another request as uri is different for subsequent int16 register
    ->useUri('tcp://127.0.0.1:5023')
    ->string(
        669,
        10,
        'username_plc2',
        function ($value, $address, $response) {
            return 'prefix_' . $value; // optional: transform value after extraction
        },
        function (\Exception $exception, Address $address, $response) {
            // optional: callback called then extraction failed with an error
            return $address->getType() === Address::TYPE_STRING ? '' : null; // does not make sense but gives you an idea
        }
    )
    ->build(); // returns array of 3 ReadHoldingRegistersRequest requests

// this will use PHP non-blocking stream io to recieve responses
$responses = (new NonBlockingClient(['readTimeoutSec' => 0.2]))->sendReadRequests($fc3);
print_r($responses);

[
    [ 'pump2_feedbackalarm_do' => true, ],
    [ 'battery3_voltage_wo' => 12, ],
    [ 'username_plc2' => 'prefix_admin', ]
]

$connection = BinaryStreamConnection::getBuilder()
    ->setHost('192.168.0.1')
    ->build();
    
$packet = new ReadHoldingRegistersRequest(256, 8); //create FC3 request packet

try {
    $binaryData = $connection->connect()->sendAndReceive($packet);

    //parse binary data to response object
    $response = ResponseFactory::parseResponseOrThrow($binaryData);
    
    //same as 'foreach ($response->getWords() as $word) {'
    foreach ($response as $word) { 
        print_r($word->getInt16());
    }
    // print registers as double words in big endian low word first order (as WAGO-750 does)
    foreach ($response->getDoubleWords() as $dword) {
        print_r($dword->getInt32(Endian::BIG_ENDIAN_LOW_WORD_FIRST));
    }
        
    // set internal index to match start address to simplify array access
    $responseWithStartAddress = $response->withStartAddress(256);
    print_r($responseWithStartAddress[256]->getBytes()); // use array access to get word
    print_r($responseWithStartAddress->getDoubleWordAt(257)->getFloat());
} catch (Exception $exception) {
    echo $exception->getMessage() . PHP_EOL;
} finally {
    $connection->close();
}

$rtuBinaryPacket = RtuConverter::toRtu(new ReadHoldingRegistersRequest($startAddress, $quantity, $slaveId));
$binaryData = $connection->connect()->sendAndReceive($rtuBinaryPacket);
$responseAsTcpPacket = RtuConverter::fromRtu($binaryData);

/**
 * Install dependency with 'composer require amphp/socket'
 *
 * This will do 'parallel' socket request with help of Amp socket library
 */

require __DIR__ . '/../vendor/autoload.php';

use ModbusTcpClient\Packet\ModbusFunction\ReadHoldingRegistersRequest;
use ModbusTcpClient\Packet\ResponseFactory;
use function Amp\Socket\connect;


$uri = 'tcp://127.0.0.1:502';
$packets = [
    new ReadHoldingRegistersRequest(256, 10),
    new ReadHoldingRegistersRequest(266, 10),
];

$promises = [];
foreach ($packets as $packet) {
    $promises[] = Amp\call(function () use ($packet, $uri) {
        /** @var \Amp\Socket\ClientSocket $socket */
        $socket = yield connect($uri);
        try {
            yield $socket->write($packet);

            $chunk = yield $socket->read(); // modbus packet is so small that one read is enough
            if ($chunk === null) {
                return null;
            }
            return ResponseFactory::parseResponse($chunk);
        } finally {
            $socket->close();
        }
    });
}

try {
    // will run multiple request in parallel using non-blocking php stream io
    $responses = Amp\Promise\wait(Amp\Promise\all($promises));
    print_r($responses);
} catch (Throwable $e) {
    print_r($e);
}