I think you must use the control for RS232 of VB that is the MSComm control.
An example to transmit data
MSComm1.CommPort = 1
MSComm1.PortOpen = True
A$ = "9600,N,8,1"
MSComm1.Settings = A$
MSComm1.InputLen = 0
A$=Chr("A")
MSComm1.Output = A$
an example to receive data
MSComm1.CommPort = 1
MSComm1.PortOpen = True
A$ = "9600,N,8,1"
MSComm1.Settings = A$
MSComm1.InputLen = 10
A$ = MSComm1.InBufferCount
If A$ > 0 Then
A$ = MSComm1.Input
Msgbox A$
End If