diff --git a/updata/prottcp.py b/updata/prottcp.py
index 260c753..a01c51f 100644
--- a/updata/prottcp.py
+++ b/updata/prottcp.py
@@ -10,7 +10,17 @@ from PyQt5.QtCore import *
 
 
 
-
+def crc8(data:bytearray):
+    crc=0
+    for j in range(len(data)):
+        crc^=data[j]
+        for i in range(8):
+            if((crc&0x01)!=0):
+                crc>>=1
+                crc^=0x8c
+            else:
+                crc>>=1
+    return crc