Qualcosa del genere ... ?

codice:
Private Sub MSComm1_OnComm()
    Dim Rx As String
    Dim ix As Long

    Rx = MSComm1.Input 
    If Len(Rx) Then 
       For ix = 1 To Len(Rx)
           Text1.Text = Text1.Text & Right$("0" & Hex$(Asc(Mid$(Rx, ix, 1))), 2)
       Next i
    End If
End Sub