An exception occurred Response null or data length too short to be valid packet!

[gupta-shrinath]

Hi There
Thanks for the library and I am new to Modbus protocol so this question might be naive. I used the library with Modbus Slave Software and it worked flawlessly but when I connect my laptop to actually devices an exception is thrown response packet to be null.
I have 2 devices connected to the RS485 to Modbus TCP Converter and the setting for the devices are
Baud Rate 9600 bits/second
Data Size 8 bits/character
Parity Odd
Port Number502
Network Protocol TCP
RS485 to Modbus TCP Convertor IP is 169.254.205.239
And here is my code
`<?php
include 'database.php';
use ModbusTcpClient\Network\BinaryStreamConnection;
use ModbusTcpClient\Packet\ModbusFunction\ReadHoldingRegistersRequest;
use ModbusTcpClient\Packet\ModbusFunction\ReadHoldingRegistersResponse;
use ModbusTcpClient\Packet\ResponseFactory;
require DIR . '/vendor/autoload.php';
//$server_ip = getHostByName(getHostName());
$server_ip = '169.254.205.239';
//echo "Server IP Address is: $server_ip";
$connection = BinaryStreamConnection::getBuilder()
->setPort(502)
->setHost($server_ip)
->build();
$startAddress = 40043;
$quantity = 10;
$packet = new ReadHoldingRegistersRequest($startAddress, $quantity);
//echo 'Packet to be sent (in hex): ' . $packet->toHex() . PHP_EOL;
try {
$binaryData = $connection->connect()
->sendAndReceive($packet);
//echo 'Binary received (in hex): ' . unpack('H*', $binaryData)[1] . PHP_EOL;
/**
* @var $response ReadHoldingRegistersResponse
*/
$response = ResponseFactory::parseResponseOrThrow($binaryData);
// echo 'Parsed packet (in hex): ' . $response->toHex() . PHP_EOL;
// echo 'Data parsed from packet (bytes):' . PHP_EOL;
print_r($response->getData());
$array = $response->getData();
$query = "SELECT * FROM holdingregister WHERE id='1' ;";
mysqli_query($con,$query);
$count = mysqli_affected_rows($con);
if($count>0) {
$sql = "UPDATE holdingregister SET register1 ='$array[1]' , register2 = '$array[3]' , register3 = '$array[5]' WHERE id = 1";
mysqli_query($con,$sql);
}
else{
$sql = "INSERT INTO holdingregister(id,register1,register2,register3) VALUES ('1',$array[1],$array[3],$array[5])";
mysqli_query($con,$sql);
}

/* foreach ($response as $word) {
print_r($word->getBytes());
}
foreach ($response->asDoubleWords() as $doubleWord) {
print_r($doubleWord->getBytes());
}
// set internal index to match start address to simplify array access
$responseWithStartAddress = $response->withStartAddress($startAddress);
print_r($responseWithStartAddress[5000]->getBytes()); // use array access to get word
print_r($responseWithStartAddress->getDoubleWordAt(5001)->getFloat());*/
} catch (Exception $exception) {
echo 'An exception occurred' . PHP_EOL;
echo $exception->getMessage() . PHP_EOL;
echo $exception->getTraceAsString() . PHP_EOL;
} finally {
$connection->close();
}`

[aldas]

1. by default unitID/SlaveId is 0. Maybe you need to use different slaveID ala 1

$slaveID = 1;
$packet = new ReadHoldingRegistersRequest($startAddress, $quantity, $slaveID);

2. maybe you need to wait a little before reading
   change from using sendAndReceive to

    $connection->connect()->send($packet);
    usleep(100000); // wait 100ms
    $binaryData = $connection->receive();

3. use wireshark to see what Modbus Slave Software sends and compare it to what is library sends.

[gupta-shrinath]

1. by default unitID/SlaveId is 0. Maybe you need to use different slaveID ala 1

$slaveID = 1;
$packet = new ReadHoldingRegistersRequest($startAddress, $quantity, $slaveID);

1. maybe you need to wait a little before reading
   change from using `sendAndReceive` to

    $connection->connect()->send($packet);
    usleep(100000); // wait 100ms
    $binaryData = $connection->receive();

1. use wireshark to see what `Modbus Slave Software` sends and compare it to what is library sends.

I tried the solutions you gave but it didn't work. Actually, the data packet sent is fine but the response packet is null for the reasons i don't know

[gupta-shrinath]

Packet to be sent (in hex): ad8500000006010300040002 Binary received (in hex): 00 An exception occurred Packet crc (\x00) does not match calculated crc (\xffff)! #0 C:\xampp\htdocs\modbus\readRegister.php(30): ModbusTcpClient\Packet\RtuConverter::fromRtu('\x00') #1 C:\xampp\htdocs\modbus\HRLoad.php(13): include('C:\xampp\htdocs...') #2 {main}

[aldas]

maybe you could try with some other client
ala

• https://www.simplymodbus.ca/RTUmaster.htm
• https://sourceforge.net/projects/easymodbustcp/

just to see if it works at all.

[gupta-shrinath]

Earlier I did a mistake I made the packet for modbus tcp while I was sending it to the modbus rtu devices.I saw the issue 'This project supports Modbus RTU' and i am facing readtimeout even on increased readtimeout sec I have posted the reply in the closed issue please kindly do take a look