diff --git a/Si5351.md b/Si5351.md
index 4302432..4fdd1f8 100644
--- a/Si5351.md
+++ b/Si5351.md
@@ -1,10 +1,22 @@
 # Frequenz setzen
 
-`f_out = f_xtal * p * m * 1/r`
+`f_out = f_xtal * p * 1/m * 1/r`
 
 * **p** PLL-Faktor, zwischen 15 und 90
 * **m** Multisynth-Faktor, zwischen 6 und 1800
 * **r** Output-Teiler `r = 2 ^ n` für 0 <= n <= 7
 
 Beispiel Code:
-https://radiotransmitter.wordpress.com/2017/02/23/a-simple-software-to-control-the-si5351a-generator-chip/
\ No newline at end of file
+https://radiotransmitter.wordpress.com/2017/02/23/a-simple-software-to-control-the-si5351a-generator-chip/
+
+# Register berechnen
+Application Note: 
+https://www.silabs.com/documents/public/application-notes/AN619.pdf
+
+Für `a + b/c = m`:
+```
+MSNx_P1 = 128 * a + floor(128 * b/c) + 512
+MSNx_P2 = 128 * b - c * floor(128 * b/c)
+MSNx_P3 = c
+```
+