Revert "ExceptionResponse for no_response_expected."

This reverts commit c03741c.

Author: janiversen

examples/client_async_calls.py

@@ -268,8 +268,7 @@ async def async_execute_diagnostic_requests(client):
     assert not rr.isError()  # test that call was OK
     rr = await client.diag_force_listen_only(device_id=DEVICE_ID, no_response_expected=True)
     assert rr.isError()  # test that call was OK, error indicate no response
-    assert not rr.dev_id
-    assert rr.exception_code == -1
+
 
 # ------------------------
 # Run the calls in groups.

pymodbus/transaction/transaction.py

@@ -127,7 +127,7 @@ def sync_execute(self, no_response_expected: bool, request: ModbusPDU) -> Modbus
             while count_retries <= self.retries:
                 self.pdu_send(request)
                 if no_response_expected:
-                    return ExceptionResponse(request.function_code, device_id=0, exception_code=-1)
+                    return ExceptionResponse(0xff)
                 try:
                     response = self.sync_get_response(request.dev_id, request.transaction_id)
                     if response.dev_id != request.dev_id:
@@ -170,7 +170,7 @@ async def execute(self, no_response_expected: bool, request: ModbusPDU) -> Modbu
                 self.response_future = asyncio.Future()
                 self.pdu_send(request)
                 if no_response_expected:
-                    return ExceptionResponse(request.function_code, device_id=0, exception_code=-1)
+                    return ExceptionResponse(0xff)
                 try:
                     response = await asyncio.wait_for(
                         self.response_future, timeout=self.comm_params.timeout_connect