I get no response from the computer on WriteSingleCoil operations

[juanchapi2]

When performing isolated read operations, my program runs without problems. The problem arises when I perform these reads after I've performed the START operation on the device. When performing the START operation, the read either takes a long time to return the response, or the program freezes.

Another aspect to keep in mind is that when performing writes, I must force the program to exit the operation via a Task, since it performs the write correctly, but the weighing equipment retains control of the program.

I think it's a problem with the weighing equipment, but I hope you can guide me and help me with anything. I remind you that I'm using a program developed in Visual Basic with Visual Studio and that I use ModbusRTU.

Greetings and sorry for the inconvenience.

[Padanian]

Some piece of software you would like to share?
Is your software on github?

[juanchapi2]

No, I don't currently have my software uploaded to Git, but here are the isolated Write and Read functions:

`Public Sub IniciarPesada(slaveID As Byte)
modbusClient.UnitIdentifier = slaveID
modbusClient.WriteSingleCoil(65534, True)
End Sub

Public Function LeerPesoNeto(slaveID As Byte) As Double
Try
modbusClient.UnitIdentifier = slaveID

    ' Leer 4 registros de 16 bits desde FFF8 (65528)
    Dim registers As Integer() = modbusClient.ReadHoldingRegisters(&HFFF8, 4)

    ' Convertir 4 registros de 16 bits en 8 bytes correctamente
    Dim bytes(7) As Byte

    For i As Integer = 0 To 3
        bytes(i * 2) = (registers(i) >> 8) And &HFF      ' High byte
        bytes(i * 2 + 1) = registers(i) And &HFF         ' Low byte
    Next

    ' Interpretar como Double (IEEE 754)
    Dim peso As Double = BitConverter.ToDouble(bytes.Reverse().ToArray(), 0)
    Return peso

Catch ex As Exception
    MessageBox.Show("Error al leer el peso neto: " & ex.Message)
    Return 0
End Try

End Function`

Read does it without any problem in the previous function and Write does the writing to the computer but it freezes and I can't regain control of the program. To do this, I used this solution, which is to control the write with a task:

`Public Sub FinalizarPesada(slaveID As Byte)
Dim cts As New Threading.CancellationTokenSource()
Dim task As Task = Task.Run(Sub()
Try
modbusClient.UnitIdentifier = slaveID
modbusClient.WriteSingleCoil(65533, True)
Catch ex As Exception
MessageBox.Show("Error: " & ex.Message)
End Try
End Sub, cts.Token)

If Not task.Wait(200) Then
    cts.Cancel()
    ' Continuar ejecución normalmente
End If

End Sub`

Up to this point everything was going well, I made the reading and the program continued, but the problem I am encountering now is that when I do the Write and then the Read, the Read freezes the program or takes a long time, which should not happen because if you do an isolated Read it takes a short time.

[harjit-S]

You are using single instance of modbusClient & calling it from two parallel threads probably. Use single thread for test case to read & write operation using loop for 5-6 times in a sequence.

[Padanian]

So at first you initiate the weighting with IniciarPesada()
Then you do the weigthing with LeerPesoNeto()
And finally you end the weight with FinalizarPesada()

I expect that after FinalizarPesada() you do IniciarPesada(), so there must be two writes in sequence, right?

[juanchapi2]

Yes, the idea is to IniciarPesada(), LeerPesoNeto() and FinalizarPesada(), but the code never reaches FinalizarPesada(), since it remains frozen in LeerPesoNeto()

[Padanian]

Why don't you start using ConvertRegistersToDouble(int[] registers)

and remove this

    ' Convertir 4 registros de 16 bits en 8 bytes correctamente
    Dim bytes(7) As Byte

    For i As Integer = 0 To 3
        bytes(i * 2) = (registers(i) >> 8) And &HFF      ' High byte
        bytes(i * 2 + 1) = registers(i) And &HFF         ' Low byte
    Next

    ' Interpretar como Double (IEEE 754)
    Dim peso As Double = BitConverter.ToDouble(bytes.Reverse().ToArray(), 0)

And try again

Also, you don't need to repeat the unit identifier here and there.
Did you try reducing the timeout?
Did you try putting some delay between reads and writes?

Please show us how you open the port to your server device.

[juanchapi2]

It still doesn't work, but now it has thrown me an exception of "No response from modbus Slave", this is my read function:
`Public Function LeerPesoNeto(slaveID As Byte) As Double
Try
modbusClient.UnitIdentifier = slaveID

    Dim registers As Integer() = modbusClient.ReadHoldingRegisters(&HFFF8, 4)

    Dim peso As Double = ModbusClient.ConvertRegistersToDouble(registers)

    Return peso

Catch ex As Exception
    MessageBox.Show("Error al leer el peso neto: " & ex.Message)
    Return 0
End Try

End Function`

I have performed several tests and what is happening is very strange, since after IniciarPesada(), when I call the reading, in the first test it sent the exception that I mentioned at the beginning, in the second it read the value correctly and in the third the program has frozen.

The problem is with the Write function and the requirement that it exit and return control of the program to me. I've tried it for 1 ms and it still doesn't work. Could you tell me how to fix this or how I can add timeouts? I remind you of the function IniciarPesada():
`Public Sub IniciarPesada(slaveID As Byte)
Dim cts As New Threading.CancellationTokenSource()
Dim task As Task = Task.Run(Sub()
Try
modbusClient.UnitIdentifier = slaveID
modbusClient.WriteSingleCoil(65534, True)
Catch ex As Exception
MessageBox.Show("Error: " & ex.Message)
End Try
End Sub, cts.Token)

If Not task.Wait(200) Then
    cts.Cancel()

End If

End Sub`

[harjit-S]

What is your slave device? Have you tried using a different device or test on modbus slave software?

[juanchapi2]

I'm using a DataControl slave device, which is a weighing device.
No, I haven't tried it with another device or with Modbus slave software. How could I do this?

[Padanian]

I think the problem is with the device.
I've used this library for ages, without problems.

[juanchapi2]

@Padanian Do you also use the task in Write operations to regain control of the program and keep it going?

[harjit-S]

You can use modbus slave software to simulate your device. ModbusTools have 30 days trails for the Modbus Slave software.

https://www.modbustools.com/download.html

[Padanian]

@Padanian Do you also use the task in Write operations to regain control of the program and keep it going?

No, never.

[juanchapi2]

Okay @Padanian @harjit-S , thank you so much for the help. The problem is 100% with the device. I'll try the simulator to see what happens. Best regards, and sorry for the inconvenience.

[harjit-S]

Also try testing your device with some different software for validation. You can use this https://github.com/harjit-S/MBConnect as well.