diff --git a/scripts/network.gd b/scripts/network.gd
index 3a73b13a..3104223f 100644
--- a/scripts/network.gd
+++ b/scripts/network.gd
@@ -21,6 +21,31 @@ class Spt25Serial extends SerialPort:
 
     func _to_string() -> String: return 'последовательный порт \"%s\" @ %d (%s)' % [self.port, self.baudrate, 'открыт' if is_open() else 'закрыт']
 
+    func get_check_sum(src: PackedByteArray) -> int:
+        var P_DIV: = 0xF0B8
+        var FCS = ~((src[2]<<8) + src[1])
+        for i in range(3, src.size()):
+            var C = src[i]
+            for j in 8:
+                if C & 1:
+                    if FCS & 1:
+                        FCS = ((FCS >> 1) | 0x8000) ^ P_DIV
+                    else:
+                        FCS = ((FCS >> 1) | 0x8000)
+                else:
+                    if FCS & 1:
+                        FCS = (FCS >> 1) ^ P_DIV
+                    else:
+                        FCS = FCS >> 1
+                C >>= 1
+            for j in 16:
+                if FCS & 1:
+                    FCS = (FCS >> 1) ^ P_DIV
+                else:
+                    FCS = FCS >> 1
+        return ~FCS
+
+
     func try_open(parsing_proc: Callable):
         if is_open():
             return Error.OK