Implement support for broadcast

umodbus/const.py

@@ -137,6 +137,9 @@
     0x4100, 0x81C1, 0x8081, 0x4040
 )
 
+#: Broadcast address
+BROADCAST_ADDR = const(0x00)
+
 
 # Code to generate the CRC-16 lookup table:
 # def generate_crc16_table():

umodbus/serial.py

@@ -64,7 +64,7 @@ def __init__(self,
                    parity=parity,
                    pins=pins,
                    ctrl_pin=ctrl_pin),
-            [addr]
+            [Const.BROADCAST_ADDR, addr]
         )
 
 
@@ -292,7 +292,7 @@ def _send(self, modbus_pdu: bytes, slave_addr: int) -> None:
     def _send_receive(self,
                       modbus_pdu: bytes,
                       slave_addr: int,
-                      count: bool) -> bytes:
+                      count: bool) -> bytes|None:
         """
         Send a modbus message and receive the reponse.
 
@@ -311,6 +311,10 @@ def _send_receive(self,
 
         self._send(modbus_pdu=modbus_pdu, slave_addr=slave_addr)
 
+        if slave_addr == Const.BROADCAST_ADDR:
+            # Do not wait for response after a broadcast
+            return None
+
         return self._validate_resp_hdr(response=self._uart_read(),
                                        slave_addr=slave_addr,
                                        function_code=modbus_pdu[0],
@@ -386,6 +390,11 @@ def send_response(self,
         :param      signed:                 Indicates if signed
         :type       signed:                 bool
         """
+
+        if slave_addr == Const.BROADCAST_ADDR:
+            # Do not reply to broadcast messages
+            return
+
         modbus_pdu = functions.response(
             function_code=function_code,
             request_register_addr=request_register_addr,