Private Sub Text1_KeyPress(KeyAscii As Integer)
 
    Select Case KeyAscii   '-- Tastenfreigabe
        Case 65 To 90: Case 97 To 122: Case 8, 44  '-- a - z, A - Z, Backspace 
        ' und Komma
        Case Else
            KeyAscii = 0: Beep
    End Select
 
   ' Nur kleines a erlaubt
' ---  If Right(Text1.Text, 1) = "," And KeyAscii <> 97 Then KeyAscii = 0: Beep
 
   ' Nur kleines a und großes A erlaubt
   If Right(Text1.Text, 1) = "," And KeyAscii <> 97 And Right(Text1.Text, 1) _
     = "," And KeyAscii <> 65 Then KeyAscii = 0: Beep
 
 
   ' am Anfang nur ein kleines a erlaubt
' ---  If Text1.SelStart = 0 And KeyAscii <> 97 Then KeyAscii = 0: Beep
 
   ' am Anfang ein kleines a und großes A erlaubt
   If Text1.SelStart = 0 And KeyAscii <> 97 And Text1.SelStart = 0 And _
     KeyAscii <> 65 Then KeyAscii = 0: Beep
 
End Sub