diff --git a/avr/common/crc8.asm b/avr/common/crc8.asm
index 3f829f9..76b0d2a 100644
--- a/avr/common/crc8.asm
+++ b/avr/common/crc8.asm
@@ -20,20 +20,23 @@
 ; @param X    pointer to data to calc crc8 for
 ; @param r18  number of bytes to calc crc8 for
 ; @param r19  polynomial to use
-; @clobbers: R16, R17, R18, R20, X
+; @clobbers: R16, R17, R18, R20, R21, X
 
 crc8Calc:
-  ldi r16, 0xff              ; start crc
+  clr r16                    ; start crc
   
 crc8Calc_loop1:
     ld r17, X+               ; running var
-    eor r16, r17
     ldi r20, 8               ; counter for loop2
-crc8Calc_loop2:
-      lsl r16
-      brcc crc8Calc_l1
+crc8Calc_loop2:       ; r16=crc so far, r17=current inbyte
+      mov r21, r16
+      lsr r16
+      eor r21, r17
+      lsr r17
+      andi r21, 1
+      breq crc8Calc_withoutPoly
       eor r16, r19
-crc8Calc_l1:
+crc8Calc_withoutPoly:
       dec r20
     brne crc8Calc_loop2
     dec r18
@@ -41,5 +44,3 @@ crc8Calc_l1:
   ret
 ; @end
 
-
-
diff --git a/avr/modules/com2/crc.asm b/avr/modules/com2/crc.asm
index 68bf2aa..e5c183e 100644
--- a/avr/modules/com2/crc.asm
+++ b/avr/modules/com2/crc.asm
@@ -66,8 +66,42 @@ com2CalcMsgChecksum:
   sbiw xh:xl, COM2_MSG_OFFS_MSGLEN
   inc r18                             ; account for dest address
   inc r18                             ; account for msg len byte
-  ldi r19, COM2_CRC8_POLYNOMIAL       ; polynomial
-  rjmp crc8Calc                       ; (R16, R17, R18, R20, X)
+  rjmp com2CrcCalc                       ; (R16, R17, R18, R20, X)
 ; @end
 
 
+
+; ---------------------------------------------------------------------------
+; @routine com2CrcCalc @global
+; calc checksum using given polynomial
+;
+; @return r16 calculated checksum
+; @return X   points directly after last checked byte
+; @param X    pointer to data to calc crc8 for
+; @param r18  number of bytes to calc crc8 for
+; @param r19  polynomial to use
+; @clobbers: R16, R17, R18, R20, X
+
+com2CrcCalc:
+  ldi r16, 0xff                 ; start crc
+  ldi r19, COM2_CRC8_POLYNOMIAL ; polynomial
+  
+com2CrcCalc_loop1:
+    ld r17, X+                  ; running var
+    eor r16, r17
+    ldi r20, 8                  ; counter for loop2
+com2CrcCalc_loop2:
+      lsl r16
+      brcc com2CrcCalc_l1
+      eor r16, r19
+com2CrcCalc_l1:
+      dec r20
+    brne com2CrcCalc_loop2
+    dec r18
+  brne com2CrcCalc_loop1
+  ret
+; @end
+
+
+
+