Merge branch 'pull/471' into dev

Author: sanjay

pymodbus/client/sync.py

@@ -539,6 +539,7 @@ def __init__(self, method='ascii', **kwargs):
         :param timeout: The timeout between serial requests (default 3s)
         :param strict:  Use Inter char timeout for baudrates <= 19200 (adhere
         to modbus standards)
+        :param handle_local_echo: Handle local echo of the USB-to-RS485 adaptor
         """
         self.method = method
         self.socket = None
@@ -553,6 +554,7 @@ def __init__(self, method='ascii', **kwargs):
         self.timeout = kwargs.get('timeout',  Defaults.Timeout)
         self._strict = kwargs.get("strict", True)
         self.last_frame_end = None
+        self.handle_local_echo = kwargs.get("handle_local_echo", False)
         if self.method == "rtu":
             if self.baudrate > 19200:
                 self.silent_interval = 1.75 / 1000  # ms

pymodbus/transaction.py

@@ -228,6 +228,10 @@ def _transact(self, packet, response_length, full=False, broadcast=False):
                 _logger.debug("Changing transaction state from 'SENDING' "
                               "to 'WAITING FOR REPLY'")
                 self.client.state = ModbusTransactionState.WAITING_FOR_REPLY
+            if self.client.handle_local_echo is True:
+                local_echo_packet = self._recv(size, full)
+                if local_echo_packet != packet:
+                    return b'', "Wrong local echo"
             result = self._recv(response_length, full)
             if _logger.isEnabledFor(logging.DEBUG):
                     _logger.debug("RECV: " + hexlify_packets(result))