habe einen code im netz gefunden und an den mega8 angepasst
sowie an die ports 3- 5 in deinem fall.

Code:
'code gefunden bei http://www.amhamberg.de
'an mega8 portb.3 bis .5 angepasst mit 8mhz
'internen takt,geändert am 28.01.2007

$regfile = "m8def.dat"
$crystal = 8000000

Ddrb = &B11111111
Portb = &B00000000


Dim A As Integer
Dim B As Integer
Dim C As Integer
Dim X As Integer
Dim Y As Integer

Dim Onoff1 As Bit
Dim Onoff2 As Bit


Declare Sub Dimmen(byval Led1 As Integer , Byval Led2 As Integer)

Do

Do
 A = Rnd(3) + 3
  B = Rnd(3) + 3

   If A <> B Then Exit Do
Loop

If Portb.a = 1 And Portb.b = 1 Then
 C = 3
  While C = A Or C = B
   Incr C
    Wend
     If Portb.c = 1 Then
      Call Dimmen(a , B)
       Else
        Call Dimmen(a , C)
     End If
Else
 Call Dimmen(a , B)
End If

Loop

End

Sub Dimmen(byval Led1 As Integer , Byval Led2 As Integer)

If Portb.led1 = 0 Then
 Onoff1 = 1
  Else
   Onoff1 = 0
End If

If Portb.led2 = 0 Then
 Onoff2 = 1
  Else
   Onoff2 = 0
End If

For X = 0 To 500
 For Y = 1 To 500
  If X > Y Then
   Portb.led1 = Onoff1
    Portb.led2 = Onoff2
     Else
      Portb.led1 = Not Onoff1
       Portb.led2 = Not Onoff2
  End If
 Next
Next
 Portb.led1 = Onoff1
  Portb.led2 = Onoff2
   Waitms 500

End Sub