Why won't this VB 6 code open the serial port?

Dim MSComm1 As MSComm

on error goto cant_open_com1

MSComm1.CommPort = 1
MSComm1.Settings = "9600,N,8,1"
MSC开发者_开发问答omm1.DTREnable = True
MSComm1.Handshaking = comRTS
MSComm1.InBufferSize = 12 + 1  ' +1 for the CR
MSComm1.RThreshold = MSComm1.InBufferSize
MSComm1.RTSEnable = True
MSComm1.InputLen = 0 ' read entire input buffer
MSComm1.InputMode = comInputModeText
MSComm1.NullDiscard = True
MSComm1.OutBufferSize = 0 ' not used, we don't write to the serial port
MSComm1.SThreshold = MSComm1.OutBufferSize
'MSComm1.ParityReplace = ?

MSComm1.PortOpen = True

Control passes to the on error handler

When you say "control passes to the error handler", did you forget to add an Exit Sub? In your comments, you say you added the New declaration, but you still having a problem? Well, I just ran this code and it had no trouble opening the port.

Private Sub Form_Load()

  Dim MSComm1 As New MSComm

  On Error GoTo cant_open_com1

  MSComm1.CommPort = 1
  MSComm1.Settings = "9600,N,8,1"
  MSComm1.DTREnable = True
  MSComm1.Handshaking = comRTS
  MSComm1.InBufferSize = 12 + 1
  MSComm1.RThreshold = MSComm1.InBufferSize
  MSComm1.RTSEnable = True
  MSComm1.InputLen = 0
  MSComm1.InputMode = comInputModeText
  MSComm1.NullDiscard = True
  MSComm1.OutBufferSize = 0
  MSComm1.SThreshold = MSComm1.OutBufferSize

  MSComm1.PortOpen = True

  Exit Sub

cant_open_com1:
    Debug.Print Err.Description

End Sub

Do not set printer on port COM1. COM1 port will be occupied by Printer in COM1 port. When use Visual Basic MSCOMM component, you do not need any printer driver. If you do set Printer in COM1 port. You can use the following code. this code will not impacted by printer setting.

Visual Basic: Open "COM1" For Output AS #1