diff --git a/avr/modules/ds18b20/main.asm b/avr/modules/ds18b20/main.asm
index 5cdab6c..93f9693 100644
--- a/avr/modules/ds18b20/main.asm
+++ b/avr/modules/ds18b20/main.asm
@@ -20,6 +20,7 @@
 .equ DS18B20_FLAGS_CONV_STARTED    = 0x01
 .equ DS18B20_FLAGS_CONV_UPDATED    = 0x02
 
+.equ DS18B20_POLYNOMIAL            = 0x8c
 
 
 ; ***************************************************************************
@@ -96,13 +97,13 @@ Ds18b20_OnTimer:
   ; conversion complete, read value, set flags
   ldi xl, LOW(ds18b20DataBuffer)
   ldi xh, HIGH(ds18b20DataBuffer)
+  in r15, SREG
   push r15
-    in r15, SREG
     cli
     rcall ds18b20ReadScratchPad
     brcc Ds18b20_OnTimer_popr15ret
-    out SREG, r15
   pop r15
+  out SREG, r15
   
   ld r16, X+                               ; copy temp from scratchpad
   sts ds18b20DataTemp, r16
@@ -116,8 +117,8 @@ Ds18b20_OnTimer:
   ret
 
 Ds18b20_OnTimer_startConversion:
+  in r15, SREG
   push r15
-    in r15, SREG
     cli
     ldi r16, DS18B20_FNCMD_CONVERT
     rcall Ds18b20_SendCommand
@@ -126,8 +127,8 @@ Ds18b20_OnTimer_startConversion:
     ori r16, DS18B20_FLAGS_CONV_STARTED
     sts ds18b20Flags, r16
 Ds18b20_OnTimer_popr15ret:
-    out SREG, r15
   pop r15
+  out SREG, r15
 Ds18b20_OnTimer_done:
   ret
 
@@ -190,11 +191,10 @@ Ds18b20_ReadRom_loop1:
     dec r23
   brne Ds18b20_ReadRom_loop1
   sbiw xh:xl, 8
-  ldi r18, 7
-  ldi r19, 0x99
-  rcall crc8Calc                  ; (R16, R17, R18, R20, X)
-  ld r17, X+
-  cp r16, r17
+  ldi r18, 8
+  ldi r19, DS18B20_POLYNOMIAL
+  rcall ds18b20Crc8Calc                  ; (R16, R17, R18, R20, R21, X)
+  tst r16
   brne Ds18b20_ReadRom_error
   sec
   ret
@@ -229,12 +229,11 @@ ds18b20ReadScratchPad_loop1:
     dec r23
   brne ds18b20ReadScratchPad_loop1
   sbiw xh:xl, 9
-  ldi r18, 8
-  ldi r19, 0x99
-  rcall crc8Calc                  ; (R16, R17, R18, R20, X)
-  ld r17, X+
-  cp r16, r17
-;  brne ds18b20ReadScratchPad_error
+  ldi r18, 9
+  ldi r19, DS18B20_POLYNOMIAL
+  rcall ds18b20Crc8Calc                  ; (R16, R17, R18, R20, R21, X)
+  tst r16
+  brne ds18b20ReadScratchPad_error
   sbiw xh:xl, 9
   sec
   ret
@@ -260,6 +259,41 @@ Ds18b20_SendTemp:
 
 
 
+; ---------------------------------------------------------------------------
+; @routine ds18b20Crc8Calc @global
+; calc crc8 checksum using given polynomial
+;
+; @return r16 crc8 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, R21, X
+
+ds18b20Crc8Calc:
+  clr r16                    ; start crc
+  
+ds18b20Crc8Calc_loop1:
+    ld r17, X+               ; running var
+    ldi r20, 8               ; counter for loop2
+ds18b20Crc8Calc_loop2:       ; r16=crc so far, r17=current inbyte
+      mov r21, r16
+      lsr r16
+      eor r21, r17
+      lsr r17
+      andi r21, 1
+      breq ds18b20Crc8Calc_withoutPoly
+      eor r16, r19
+ds18b20Crc8Calc_withoutPoly:
+      dec r20
+    brne ds18b20Crc8Calc_loop2
+    dec r18
+  brne ds18b20Crc8Calc_loop1
+  ret
+; @end
+
+
+
 DS18B20_END:
 .equ MODULE_SIZE_DS18B20 = DS18B20_END-DS18B20_BEGIN