Transaction_id for serial == 0. (#2208)

Author: janiversen

pymodbus/framer/rtu_framer.py

@@ -160,7 +160,7 @@ def check_frame(self):
             if (result := self.decoder.decode(data)) is None:
                 raise ModbusIOException("Unable to decode request")
             result.slave_id = self._header["uid"]
-            result.transaction_id = self._header["tid"]
+            result.transaction_id = 0
             self._buffer = self._buffer[self._header["len"] :]
             Log.debug("Frame advanced, resetting header!!")
             callback(result)  # defer or push to a thread?
@@ -174,8 +174,7 @@ def buildPacket(self, message):
         packet = self.message_handler.encode(data, message.slave_id, message.transaction_id)
 
         # Ensure that transaction is actually the slave id for serial comms
-        if message.slave_id:
-            message.transaction_id = message.slave_id
+        message.transaction_id = 0
         return packet
 
     def sendPacket(self, message):