[Bug]: Modbus Over TCP Reading Float Value in Negative Issue

[Balaji-Sundar]

What happened?

Modbus Over TCP Reading Float Value in Negative Issue. Actual value is 1.93e+07
public static void main(String[] args) {
try {
String ip = "10.7.10.1";
int port = 502;
int slaveId = 2;
int requestTimeOut = 10000;
String payLoadByteOrder = "LITTLE_ENDIAN_BYTE_SWAP";
String connectionUrl = String.format("modbus-tcp:tcp://%s:%d?unit-identifier=%d&request-timeout=%d&default-payload-byte-order=%s", ip, port, slaveId, requestTimeOut, payLoadByteOrder);
try (PlcConnection plcConnection = new DefaultPlcDriverManager().getConnection(connectionUrl)) {
if (!plcConnection.getMetadata().isReadSupported()) {
System.out.println("This connection doesn't support reading.");
}
PlcReadRequest.Builder builder = plcConnection.readRequestBuilder();
builder.addTagAddress("value1", "holding-register:159:REAL[2]");
PlcReadRequest readRequest = builder.build();
PlcReadResponse response = readRequest.execute().get();
System.out.println("response = " + response.toString());
for (String tagName : response.getTagNames()) {
System.out.println("Tag: " + tagName);
System.out.println("Response code for " + tagName + ": " + response.getResponseCode(tagName));
int numValues = response.getNumberOfValues(tagName);
System.out.println("numValues = " + numValues);
if (response.getResponseCode(tagName) == PlcResponseCode.OK) {
System.out.println("response = " + response.getTag(tagName));
System.out.println("response = " + response.getFloat(tagName));
//response.getAllBytes(tagName).stream().map(HexUtil::toHex).map(hex -> "Register Value: " + hex).forEach(System.out::println);
} else {
System.out.println("Error[" + tagName + "]: " + response.getResponseCode(tagName).name());
}
}
}
} catch (Exception e) {
System.out.println("e = " + e);
}
}
Output:
response = org.apache.plc4x.java.spi.messages.DefaultPlcReadResponse@6a47b187
Tag: value1
Response code for value1: OK
numValues = 2
response = ModbusTagHoldingRegister {address=158, quantity=2, dataType=REAL }
response = -7.128774E35

Version

v0.12.0

Programming Languages

• plc4j
• plc4go
• plc4c
• plc4net

Protocols

• AB-Ethernet
• ADS /AMS
• BACnet/IP
• CANopen
• DeltaV
• DF1
• EtherNet/IP
• Firmata
• KNXnet/IP
• Modbus
• OPC-UA
• S7

[chrisdutz]

Well. Modbus technically doesn't know floats. We just interpret four bytes as a float. Possibly your system uses a different encoding?

What type of device are you using?

[Balaji-Sundar]

We are using USR-TCP232-410S device to query RS-485 supported modbus device. Baud Rate : 9600 Data Size : 8bit Parity : Even Stop bits : 1 Flow Control : None Regards

…

-S.Balaji

On Sat, Feb 1, 2025, 21:46 Christofer Dutz ***@***.***> wrote: Well. Modbus technically doesn't know floats. We just interpret four bytes as a float. Possibly your system uses a different encoding? What type of device are you using? — Reply to this email directly, view it on GitHub <#1997 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ADNAYAZOTSA76TCBELTIBQD2NTXPDAVCNFSM6AAAAABWJCFUR6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMMRZGAYTENZUHE> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[chrisdutz]

Could you please do a wireshark capture of your attempt to read the float value as well as which value you expect it to be? Then I think we could have a look.

[Balaji-Sundar]

I find out the some of energy meters having "LITTLE_ENDIAN_BYTE_SWAP" encoding. Current version does not have encoding support. When can we have 0.13.0 release.

[chrisdutz]

Could you please double check, if it works with the latest development version? There were plans to do a new release pretty soon.

[Balaji-Sundar]

I have tried 0.13.0.SNAPSHOT version. I am getting Timeout exception.
String ip = "10.7.10.1";
int port = 502;
int slaveId = 2;
int requestTimeOut = 5000;
String payLoadByteOrder = "LITTLE_ENDIAN_BYTE_SWAP";
//String connectionUrl = String.format("modbus-tcp://%s:%d?unit-identifier=%d&request-timeout=%d&default-payload-byte-order=%s", ip, port, slaveId, requestTimeOut, payLoadByteOrder);
.addTagAddress("value1", "holding-register:159:REAL[2]{byte-order:'LITTLE_ENDIAN_BYTE_SWAP'}")

[chrisdutz]

I guess without a wireshark capture, I'd just be guessing.