Now You Can Have Robust Data Logging for Free – Part 8

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Now You Can Have Robust Data Logging for Free – Part 1
Now You Can Have Robust Data Logging for Free – Part 2
Now You Can Have Robust Data Logging for Free – Part 3
Now You Can Have Robust Data Logging for Free – Part 4
Now You Can Have Robust Data Logging for Free – Part 5
Now You Can Have Robust Data Logging for Free – Part 6
Now You Can Have Robust Data Logging for Free – Part 7
Now You Can Have Robust Data Logging for Free – Part 8

 

Computer Program Visual Basic (VB6) Continue

The display part of the program is done, and we have reviewed the Modbus TCP protocol. It is now time to start the VB6 code. Let’s discuss how the logic will work.


1. The user selects ‘Start Logging.’
2. The timer for the interval between communications is stopped.
3. The IP address is used to open the Winsock connection. If the reference is made, then the background color of the IP Address will turn green, and we will continue to step 4. If the contact already exists, then continue to step 4. If the connection cannot be made, the background color is red, and further execution is stopped. The program will continue at step 1.
4. The following sequence of commands is made: Determine what command to send.

  • Read the Daily Production Log and Minute Log Pointers (MHR1 and MHR2 )
  • If MHR2 (Minute Log Pointer ) > 670, then
    • Request the Minute Log starting at MHR670 and keep incrementing by ten until the last location is requested.
    • Write the value of 670 into MHR2 (Reset the pointer)
  • If MHR1 (Daily Production Log Pointer > 30, then
    • Request the Daily Production Log starting at MHR30 and keep incrementing by 20 until the last location is requested.
    • Write the value of 30 into MHR1 (Reset the pointer)
  • Read the current Minute Log information starting at MHR660
  • Read the current Daily Production Log information starting at MHR10
Once the command is sent, a timer is set to determine if communications have been lost.
Set the timer for the interval between communications. 5. If the timer for communications is lost, go to step 3. Repeat the last command.
6. Turn off the timer to determine if communications have been lost. Read the information from the Winsock tool. If the data needs to be stored, then update the database.

The above is the general program flow for the program.

Here are our variables:

Dim MbusQuery
Public MbusResponse As String
Dim MbusByteArray(255) As Byte
Public MbusStatus As Integer
Public ProductionPointer As Integer
Public MinutePointer As Integer  

Private Sub Command1_Click()
Timer1.Enabled = False’ Stop the interval between reads to the PLC

Timer 1 controls the time between intervals of communication to the PLC.

Dim StartTime
If Winsock1.State <> 7 Then
    If (Winsock1.State <> sckClosed) Then
        Winsock1.Close
    End If
    Winsock1.RemoteHost = Text1.Text’ Set IP Address
    Winsock1.Connect
    
    StartTime = Timer’ Use the timer to determine if a connection cannot be made.
    
    Do While ((Timer < StartTime + 2) And (Winsock1.State <> 7))
        DoEvents
    Loop
    If (Winsock1.State = 7) Then
       Text1.BackColor = &HFF00& ‘Change the background color to green
    Else
       Text1.BackColor = &HFF ‘Change the background color to red
       Exit Sub
    End If
End If

Here is the code to control Winsock1. The IP address entered in Text1 is used to set the RemoteHost. We then check for the state of the Winsock1. The following are the different states that Winsock1 can be in:

Constant Value Description
sckClosed 0 Default. Closed
sckOpen 1 Open
sckListening 2 Listening
sckConnectionPending 3 Connection pending
sckResolvingHost 4 Resolving host
sckHostResolved 5 Host resolved
sckConnecting 6 Connecting
sckConnected 7 Connected
sckClosing 8 The peer is closing the connection
sckError 9 Error
Here is the information that we will need to read and write to the MHR registers in the Do-More PLC.

‘Read the information

‘0000:    Transaction Identifier
‘0000:    Protocol Identifier
‘0006:    Message Length (6 bytes to follow)
’00:      The Unit Identifier
’03:      The Function Code (read MHR Read Holding Registers)
‘0000:    The Data Address of the first register
‘0002:    The number of records to write
‘Write the information
‘0000:    Transaction Identifier
‘0000:    Protocol Identifier
‘0009:    Message Length (6 bytes to follow)
’01:      The Unit Identifier
’16:      The Function Code (read Analog Output Holding Registers)
‘0000:    The Data Address of the first register
‘0001:    The number of registers to write
’02:      The number of data bytes to follow
‘0030     The number to put into the register
All of the information will be bytes of data. The maximum value in a byte is 256. If we need to send a value of 600, then the two bytes of data will be:
600/256 = 2.34
The most significant byte is 02
600 – (256*2) = 88
The least significant byte is 88
So the information we need to send through Winsock1 would be Chr(2) and Chr(88) to represent the value of 600.

In part 9, we will continue with writing the VB6 program. We will start reading and writing the information to the PLC.
If you have any questions or need further information, please get in touch with me.
Thank you,
Garry



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