Modbus TCP and RTU over TCP protocol client
, (*1)
- Modbus TCP/IP specification: http://www.modbus.org/specs.php
- Modbus TCP/IP and RTU simpler description: http://www.simplymodbus.ca/TCP.htm
Installation
Use Composer to install this library as dependency., (*2)
composer require aldas/modbus-tcp-client
Supported functions
Utility functions
Requirements
- PHP 8.0+
- Release 2.4.0 was last to support PHP 7 (7.4 might work with v3.0.0)
- Release 0.2.0 was last to support PHP 5.6
Intention
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), (*3)
Addresses
This library uses PDU / protocol level address numbers (0 is very first register/coil). This is different from numbering
schemes (0xxxxx, 1xxxxx, 3xxxxx, and 4xxxxx). The x denotes coil or register address starting from 1., (*4)
So when your documentation gives you address as 300102 you should interpret it in this library context as: FC3, address 101, (*5)
Endianness
Applies to multibyte data that are stored in Word/Double/Quad word registers basically everything
that is not (u)int16/byte/char., (*6)
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, (*7)
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), (*8)
Default (global) endianess used for parsing can be changed with:, (*9)
Endian::$defaultEndian = Endian::BIG_ENDIAN_LOW_WORD_FIRST;
For non-global cases see API methods argument list if method support using custom endianess., (*10)
See Endian.php for additional info and Types.php for supported data types., (*11)
Data types
Modbus is binary protocol which revolves about addresses of Registers/Word (16bit, 2 byte of data) and Coils (1 bit of data).
Coils are booleans but Register/Word or multiple Registers can hold different data types. Following is ways to access different
data types from Registers:, (*12)
Most of the for data types have optional arguments for providing Endian type. By default data is parsed as being Big Endian Low Word first endian., (*13)
Exaple: getting uint32 value as Little Endian Low Word First, (*14)
$dword->getUInt32(Endian::LITTLE_ENDIAN | Endian::LOW_WORD_FIRST);
1bit - 16bit data types
1-16bit data types are hold by Word class which hold 2 bytes of data., (*15)
$address = 100;
$word = $response->getWordAt($address);
Following methods exists to get different types out of single Word instance:
* boolean - 1bit, true/false, $word->isBitSet(11)
* byte - 8bit, 1 byte, range 0 to 255
* first byte of Word (0) $word->getHighByteAsInt()
* last byte of Word (1) $word->getLowByteAsInt()
* uint16 - 16bit, 2 byte, range 0 to 65535 $word->getUInt16()
* int16 - 16bit, 2 byte, range -32768 to 32767 $word->getInt16(), (*16)
and following additional methods:
* $word->getBytes() return Words as array of 2 integers (0-255), (*17)
32bit data types
17-32bit data types are hold by DoubleWord class which hold 4 bytes of data., (*18)
$address = 100;
$dword = $response->getDoubleWordAt($address);
Following methods exists to get different types out of single DoubleWord instance:
* uint32 - 32bit, 4 bytes, range 0 to 4294967295, $dword->getUInt32()
* int32 - 64bit, 8 bytes, range -2147483648 to 2147483647, $dword->getInt32()
* float - 64bit, 8 bytes, range -3.4e+38 to 3.4e+38, $dword->getFloat(), (*19)
and following additional methods:
* $dword->getBytes() return DoubleWord as array of 4 integers (0-255)
* $dword->getHighBytesAsWord() returns first 2 bytes as Word
* $dword->getLowBytesAsWord() returns last 2 bytes as Word, (*20)
64bit data types
64bit data types are hold by QuadWord class which hold 8 bytes of data.
NB: 64-bit PHP supports only up to 63-bit (signed) integers., (*21)
$address = 100;
$qword = $response->getQuadWordAt($address);
Following methods exists to get different types out of single QuadWord instance:
* uint32 - 64bit, 8 bytes, range 0 to 9223372036854775807, $dword->getUInt64()
* int32 - 64bit, 8 bytes, range -9223372036854775808 to 9223372036854775807, $dword->getInt64()
* double - 64bit, 8 bytes, range 2.2250738585072e-308 to 1.7976931348623e+308, $dword->getDouble(), (*22)
and following additional methods:
* $qword->getBytes() return QuadWord as array of 8 integers (0-255)
* $qword->getHighBytesAsDoubleWord() returns first 4 bytes as DoubleWord
* $qword->getLowBytesAsDoubleWord() returns last 4 bytes as DoubleWord, (*23)
Strings
ASCII (8bit character) string can be extracted from response as utf-8 string, (*24)
$address = 20;
$length = 10;
$string = $response->getAsciiStringAt($address, $length);
Example of Modbus TCP (fc3 - read holding registers)
Some of the Modbus function examples are in examples/ folder, (*25)
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', (*26)
Request multiple packets with higher level API:, (*27)
$address = 'tcp://127.0.0.1:5022';
$unitID = 0; // also known as 'slave ID'
$fc3 = ReadRegistersBuilder::newReadHoldingRegisters($address, $unitID)
->unaddressableRanges([[100,110], [1512]])
->bit(256, 15, 'pump2_feedbackalarm_do')
// will be split into 2 requests as 1 request can return only range of 124 registers max
->int16(657, 'battery3_voltage_wo')
// will be another request as uri is different for subsequent int16 register
->useUri('tcp://127.0.0.1:5023')
->string(
669,
10,
'username_plc2',
function ($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
$responseContainer = (new NonBlockingClient(['readTimeoutSec' => 0.2]))->sendRequests($fc3);
print_r($responseContainer->getData()); // array of assoc. arrays (keyed by address name)
print_r($responseContainer->getErrors());
Response structure, (*28)
[
[ 'pump2_feedbackalarm_do' => true, ],
[ 'battery3_voltage_wo' => 12, ],
[ 'username_plc2' => 'prefix_admin', ]
]
Low level - send packets:, (*29)
$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();
}
Example of Modbus RTU over TCP
Difference between Modbus RTU and Modbus TCP is that:, (*30)
- 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, (*31)
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., (*32)
$rtuBinaryPacket = RtuConverter::toRtu(new ReadHoldingRegistersRequest($startAddress, $quantity, $slaveId));
$binaryData = $connection->connect()->sendAndReceive($rtuBinaryPacket);
$responseAsTcpPacket = RtuConverter::fromRtu($binaryData);
Example of Modbus RTU over USB to Serial (RS485) adapter
See Linux example in 'examples/rtu_usb_to_serial.php', (*33)
Example of Modbus RTU over TCP + higher level API usage
See example in 'examples/rtu_over_tcp_with_higherlevel_api.php', (*34)
Example of non-blocking socket IO with ReactPHP/Amp (i.e. modbus request are run in 'parallel')
Example Modbus server (accepting requests) with ReactPHP
Try communication with PLCs quickly using php built-in web server
Examples folder has index.php which can be used with php built-in web server to test
out communication with our own PLCs., (*35)
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., (*36)
Changelog
See CHANGELOG.md, (*37)
Tests
- 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', (*38)
Static analysis
Run PHPStan analysis compose check, (*39)
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