- Modbus TCP/IP specification: http://www.modbus.org/specs.php
- Modbus TCP/IP and RTU simpler description: http://www.simplymodbus.ca/TCP.htm
Use Composer to install this library as dependency.
composer require aldas/modbus-tcp-client
- FC1 - Read Coils (ReadCoilsRequest / ReadCoilsResponse)
- FC2 - Read Input Discretes (ReadInputDiscretesRequest / ReadInputDiscretesResponse)
- FC3 - Read Holding Registers (ReadHoldingRegistersRequest / ReadHoldingRegistersResponse)
- FC4 - Read Input Registers (ReadInputRegistersRequest / ReadInputRegistersResponse)
- FC5 - Write Single Coil (WriteSingleCoilRequest / WriteSingleCoilResponse)
- FC6 - Write Single Register (WriteSingleRegisterRequest / WriteSingleRegisterResponse)
- FC15 - Write Multiple Coils (WriteMultipleCoilsRequest / WriteMultipleCoilsResponse)
- FC16 - Write Multiple Registers (WriteMultipleRegistersRequest / WriteMultipleRegistersResponse)
- PHP 7.0+
- Release 0.2.0 was last to support PHP 5.6
This library is influenced by phpmodbus library and meant to be provide decoupled Modbus protocol (request/response packets) and networking related features so you could build modbus client with our own choice of networking code (ext_sockets/streams/Reactphp/Amp asynchronous streams) or use library provided networking classes (php Streams)
Applies to multibyte data that are stored in Word/Double/Quad word registers basically everything that is not (u)int16/byte/char.
So if we receive from network 0x12345678 (bytes: ABCD) and want to convert that to a 32 bit register there could be 4 different ways to interpret bytes and word order depending on modbus server architecture and client architecture. NB: TCP, and UDP, are transmitted in big-endian order so we choose this as base for examples
Library supports following byte and word orders:
- Big endian (ABCD - word1 = 0x1234, word2 = 0x5678)
- Big endian low word first (CDAB - word1 = 0x5678, word2 = 0x1234) (used by Wago-750)
- Little endian (DCBA - word1 = 0x3412, word2 = 0x7856)
- Little endian low word first (BADC - word1 = 0x7856, word2 = 0x3412)
See Endian.php for additional info and Types.php for supported data types.
Some of the Modbus function examples are in examples/ folder
Advanced usage:
- command line poller with ReachPHP examples/example_cli_poller.php
- send/recieve packets parallel using non-blocking IO:
- using ReactPHP see 'examples/example_parallel_requests_reactphp.php'
- using Amp see 'examples/example_parallel_requests_amp.php'
Request multiple packets with higher level API:
$fc3 = ReadRegistersBuilder::newReadHoldingRegisters('tcp://127.0.0.1:5022')
->bit(256, 15, 'pump2_feedbackalarm_do')
// will be split into 2 requests as 1 request can return only range of 124 registers max
->int16(657, 'battery3_voltage_wo')
// will be another request as uri is different for subsequent int16 register
->useUri('tcp://127.0.0.1:5023')
->string(
669,
10,
'username_plc2',
function ($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
$responses = (new NonBlockingClient(['readTimeoutSec' => 0.2]))->sendRequests($fc3);
print_r($responses);
Response structure
[
[ 'pump2_feedbackalarm_do' => true, ],
[ 'battery3_voltage_wo' => 12, ],
[ 'username_plc2' => 'prefix_admin', ]
]
Low level - send packets:
$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();
}
Difference between Modbus RTU and Modbus TCP is that:
- RTU header contains only slave id. TCP/IP header contains of transaction id, protocol id, length, unitid
- RTU packed has 2 byte CRC appended
See http://www.simplymodbus.ca/TCP.htm for more detailsed explanation
This library was/is originally meant for Modbus TCP but it has support to convert packet to RTU and from RTU. See this examples/rtu.php for example.
$rtuBinaryPacket = RtuConverter::toRtu(new ReadHoldingRegistersRequest($startAddress, $quantity, $slaveId));
$binaryData = $connection->connect()->sendAndReceive($rtuBinaryPacket);
$responseAsTcpPacket = RtuConverter::fromRtu($binaryData);
Example of non-blocking socket IO with https://github.com/amphp/socket
/**
* 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);
}
Examples folder has index.php which can be used with php built-in web server to test out communication with our own PLCs.
git clone https://github.com/aldas/modbus-tcp-client.git
cd modbus-tcp-client
composer install
php -S localhost:8080 -t examples/
Now open http://localhost:8080 in browser. See additional query parameters from index.php.
- all
composer test
- unit tests
composer test-unit
- integration tests
composer test-integration
For Windows users:
- all
vendor/bin/phpunit
- unit tests
vendor/bin/phpunit --testsuite 'unit-tests'
- integration tests
vendor/bin/phpunit --testsuite 'integration-tests'