Despatch Protocol Plus Modbus Communications User Manual

Page 51

Chromalox Instruments and Controls

A-51643 Rev. 6 10/06/03

CRCWord = GetCRC(TxMessage)

'add the CRC bytes to the message:

TxMessage = TxMessage & Chr(CRCWord - Int(CRCWord / 256) * 256)

TxMessage = TxMessage & Chr(Int(CRCWord / 256))

'clear status text display:

Text1 = ""

'clear the receive data buffer:

RxMessage = ""

'send the message out the COM port:

frmComm.comMain.Output = TxMessage

End Sub

The reply message is received using the following code placed to respond to the MSComm device‘s

‗OnComm‘ event:

Private Sub comMain_OnComm()

Dim CRCValue As Long

Dim NewBuffer As String

Dim RxCount As Integer

Dim i As Integer

Select Case comMain.CommEvent

Case comEvReceive

'Read serial data bytes:

NewBuffer = comMain.Input

'Build up RxMessage

RxMessage = RxMessage & NewBuffer

'Check RxMessage to see if it's complete - the length of each expected reply