tem.

pymodbus/message/ascii.py

@@ -17,7 +17,7 @@ class MessageAscii(MessageBase):
     r"""Modbus ASCII Frame Controller.
 
         [ Start ][Address ][ Function ][ Data ][ LRC ][ End ]
-          1c        2c         2c         Nc     2c      2c
+          1c        2c         2c         Nc     1c      2c
 
         * data can be 0 - 2x252 chars
         * end is "\\r\\n" (Carriage return line feed), however the line feed
@@ -40,22 +40,23 @@ def decode(self, data: bytes) -> tuple[int, int, int, bytes]:
         if (used_len := len(data)) < 10:
             Log.debug("Short frame: {} wait for more data", data, ":hex")
             return 0, 0, 0, self.EMPTY
-        if data[0] != int(self.START):
+        if data[0:1] != self.START:
             if (start := data.find(self.START)) != -1:
                 used_len = start
             Log.debug("Garble data before frame: {}, skip until start of frame", data, ":hex")
             return used_len, 0, 0, self.EMPTY
         if not (used_len := data.find(self.END)):
             Log.debug("Incomplete frame: {} wait for more data", data, ":hex")
             return 0, 0, 0, self.EMPTY
+        lrc = int(data[used_len - 2: used_len], 16)
+        msg = a2b_hex(data[1 : used_len - 2])
+        if not self.check_LRC(msg, lrc):
+            Log.debug("LRC wrong in frame: {} skipping", data, ":hex")
+            return used_len+2, 0, 0, self.EMPTY
 
         dev_id = int(data[1:3], 16)
-        lrc = int(data[used_len - 2 : used_len], 16)
-        data = a2b_hex(data[1 : used_len - 2])
-        if not self.check_LRC(data, lrc):
-            Log.debug("LRC wrong in frame: {} skipping", data, ":hex")
-            return used_len+1, 0, 0, self.EMPTY
-        return used_len+1, dev_id, 0, data
+        _fc = int(data[3:5], 16).to_bytes(1,'big')
+        return used_len+2, 0, dev_id, msg
 
     def encode(self, data: bytes, device_id: int, _tid: int) -> bytes:
         """Decode message."""

pymodbus/message/message.py

@@ -76,10 +76,17 @@ def __init__(self,
 
     def callback_data(self, data: bytes, addr: tuple | None = None) -> int:
         """Handle received data."""
-        used_len, tid, device_id, data = self.msg_handle.decode(data)
-        if data:
-            self.callback_request_response(data, device_id, tid)
-        return used_len
+        tot_len = len(data)
+        start = 0
+        while True:
+            used_len, tid, device_id, data = self.msg_handle.decode(data[start:])
+            if data:
+                self.callback_request_response(data, device_id, tid)
+            if not used_len:
+                return used_len
+            start += used_len
+            if start == tot_len:
+                return tot_len
 
     # --------------------- #
     # callbacks and helpers #

test/message/test_ascii.py

@@ -21,6 +21,11 @@ def test_check_LRC(self):
         data = struct.pack(">HHHH", 0x1234, 0x2345, 0x3456, 0x4567)
         assert MessageAscii.check_LRC(data, 0x1C)
 
+    def test_check_noLRC(self):
+        """Test check_LRC."""
+        data = struct.pack(">HHHH", 0x1234, 0x2345, 0x3456, 0x4567)
+        assert not MessageAscii.check_LRC(data, 0x0C)
+
     def test_compute_LRC(self):
         """Test compute_LRC."""
         data = struct.pack(">HHHH", 0x1234, 0x2345, 0x3456, 0x4567)
@@ -32,5 +37,28 @@ def test_roundtrip_LRC(self):
         assert MessageAscii.compute_LRC(data) == 0x1c
         assert MessageAscii.check_LRC(data, 0x1C)
 
-    def test_decode(self, frame):
+    @pytest.mark.parametrize(
+        ("packet", "used_len", "id", "res"),
+        [
+            (b":010100010001FC\r\n", 17, 1, b'\x00\x01\x00\x00'),
+        ],
+    )
+    def test_decode(self, frame, packet, used_len, id, res):
         """Test decode."""
+        res_len, tid, dev_id, data = frame.decode(packet)
+        assert res_len == len(packet)
+        assert not tid
+        assert dev_id == id
+        assert data == res
+
+
+    # OK: b":010100010001FC\r\n"
+    # OK: b':00010001000AF4\r\n'
+    # OK: b':01010001000AF3\r\n'
+    # NO: b':01270001000ACD\r\n'
+    # OK: b':61620001000AF4\r\n'
+    # remember:
+    # -- split packet
+    # -- double packet
+    # -- garble data in front
+    # -- garble data after