ReturnVal = PviWriteRequest(pPviObj(IDC_PVI_NAME_PVAR1 + _
          SelectedItem).LinkId, POBJ_ACC_DATA, WriteValue, _
                Len(WriteValue), AddressOf OnWriteResponse, SET_PVICALLBACK, _
                pPviObj(IDC_PVI_NAME_PVAR1 + SelectedItem).EventMessage)
    If ReturnVal Then
        MsgBox "Error writing Pv" & SelectedItem & " E#" & ReturnVal
    End If

 Public Sub OnWriteResponse(ByVal WPARAM As Long, ByVal LPARAM As Long)
    Dim ReturnVal As Integer
 
    ' // acknowledge write response messages
    PviWriteResponse(WPARAM)
  End Sub

Declare Function PviWriteRequest Lib "PviCom.dll" (ByVal LinkId As Long, _
                              ByVal Access As Long, ByRef pData As Any, _
                              ByVal DataLen As Long, ByVal hReqMsg As Long, _
                              ByVal ReqMsgNum As Long, ByVal ReqParam As Long) _
                              As Long

ReturnVal = PviWriteRequest(..., AddressOf OnWriteResponse, ...)