edit

modbus_tk/modbus.py

@@ -156,7 +156,8 @@ class Master(object):
         """
 
         if isinstance(function_code, str):
-            request = bytes.fromhex(function_code)
+            #request = bytes.fromhex(function_code)
+            request = function_code.encode()
             response = self._handle(request, expected_length);
             return self._result(response)
 

modbus_tk/modbus_rtu.py

@@ -126,6 +126,7 @@ class RtuMaster(Master):
     def _handle(self, request, expected_length):
         print(request)
         self._serial.write(request)
+        self._serial.flush()
         print(expected_length)
         response = self._serial.read(expected_length)
         print(response)