Despatch Protocol Plus Modbus Communications - Manual (Page 49)

Chromalox Instruments and Controls
A-51643 Rev. 6 10/06/03 43
'initialize the CRC register:
CRCValue = 65535
For i = 1 To MLength
'this routine is called for each character of a message
CRCValue = CRCValue Xor CInt(Asc(Mid(MBuffer, i, 1)))
'for each bit in the new character,
'do this loop:
For j = 1 To 8
'determine if LSB is now a 1:
LsbSet = ((CRCValue And 1) = 1)
'shift the crc (buffer) one bit to the right:
CRCValue = Int(CRCValue / 2)
'if LSB was a 1,
If LsbSet Then
'XOR buffer value with the CRC polynomial:
CRCValue = CRCValue Xor 40961 '&HA001
End If
Next j
Next i
GetCRC = CRCValue
End Function
The following code, called in the form‘s Load procedure, is used to initialize the COM port:
Private Sub Form_Load()
'make sure the port is closed:
If frmComm.comMain.PortOpen Then frmComm.comMain.PortOpen = False
'select desired COM port:
frmComm.comMain.CommPort = 1 '1=COM1, etc.