diff --git a/AHT20_sensor_control/crc8_helper.py b/AHT20_sensor_control/crc8_helper.py
index 5401ee8..2f4bf1e 100644
--- a/AHT20_sensor_control/crc8_helper.py
+++ b/AHT20_sensor_control/crc8_helper.py
@@ -13,14 +13,38 @@
 
 # Data and CRC taken from AHT20, use this for testing?
 TEST_DATA = [[28, 184, 245, 165, 156, 208, 163], [28, 185, 16, 149, 156, 83, 112], [
-    28, 184, 249, 85, 156, 114, 213], [28, 185, 9, 53, 156, 54, 45], [28, 185, 70, 117, 156, 189, 33]
-, [28, 185, 64, 165, 156, 61, 209]]
+    28, 184, 249, 85, 156, 114, 213], [28, 185, 9, 53, 156, 54, 45], [28, 185, 70, 117, 156, 189, 33], [28, 185, 64, 165, 156, 61, 209]]
+
+
+def mod2_division_8bits(a, b, number_of_bytes, init_value):
+    "calculate mod2 division in 8 bits. a mod b. init_value is for crc8 init value."
+    head_of_a = 0x80
+    # Processiong a
+    a = a << 8
+    # Preprocessing head_of_a
+    for i in range(0, number_of_bytes):
+        head_of_a = head_of_a << 8
+        b = b << 8
+        init_value = init_value << 8
+    a = a ^ init_value
+    while (head_of_a > 0x80):
+        # Find a 1
+        if (head_of_a & a):
+            head_of_a = head_of_a >> 1
+            b = b >> 1
+            a = a ^ b
+        else:
+            head_of_a = head_of_a >> 1
+            b = b >> 1
+        print("a:{0}\thead of a:{1}\tb:{2}".format(
+            bin(a), bin(head_of_a), bin(b)))
+    return a
 
 
 def AHT20_crc8_check(all_data_int, init_value=0xFF):
     """
     The input data shoule be:
-    Status Humidity0 Humidity1 Humidity2|Temperature0 Temperature1 Temperature2 CRCCode
+    Status Humidity0 Humidity1 Humidity2|Temperature0 Temperature1 Temperature2 CRCCode.
     In python's int64.
     """
     # Preprocess all the data and CRCCode from AHT20
@@ -28,14 +52,13 @@ def AHT20_crc8_check(all_data_int, init_value=0xFF):
     # Preprocessing the first data (status)
     DATA_FROM_AHT20 = DATA_FROM_AHT20 | all_data_int[0]
     print(bin(DATA_FROM_AHT20))
-    DATA_FROM_AHT20 = DATA_FROM_AHT20 ^ init_value
-    print(bin(DATA_FROM_AHT20))
-    for i_data in range(1, N_DATA + N_CRC):
-        DATA_FROM_AHT20 = DATA_FROM_AHT20 << 8 | all_data_int[i_data]
+    for i_data in range(1, N_DATA):
+        DATA_FROM_AHT20 = (DATA_FROM_AHT20 << 8) | all_data_int[i_data]
     print(bin(DATA_FROM_AHT20))
-    mod_value = DATA_FROM_AHT20 % CRC_DEVIDE_NUMBER
+    mod_value = mod2_division_8bits(
+        DATA_FROM_AHT20, CRC_DEVIDE_NUMBER, len(all_data_int) - 1, init_value)
     print(mod_value)
-    if (mod_value == 0):
+    if (mod_value == all_data_int[-1]):
         return True
     else:
         return False
@@ -44,6 +67,21 @@ def AHT20_crc8_check(all_data_int, init_value=0xFF):
 def AHT20_crc8_calculate(all_data_int):
     pass
 
+
+def CRC8_check(all_data_int, init_value=0x00):
+    divider = 0x107
+    DATA_FOR_CHECK = all_data_int[0]
+    for data in all_data_int[1:-1]:
+        DATA_FOR_CHECK = (DATA_FOR_CHECK << 8) | data
+    remainder = mod2_division_8bits(
+        DATA_FOR_CHECK, divider, len(all_data_int) - 1, init_value)
+    if (remainder == all_data_int[-1]):
+        return True
+    else:
+        return False
+
+
 if __name__ == "__main__":
+    print(CRC8_check([0x66, 0x44, 0x33, 0x22, 0x24], 0))
     for data in TEST_DATA:
-        AHT20_crc8_check(data, INIT)
\ No newline at end of file
+        print(AHT20_crc8_check(data, INIT))