diff --git a/plc4go/internal/plc4go/bacnetip/readwrite/model/APDUComplexAck.go b/plc4go/internal/plc4go/bacnetip/readwrite/model/APDUComplexAck.go
index 8067857bcb5..85820d6dc44 100644
--- a/plc4go/internal/plc4go/bacnetip/readwrite/model/APDUComplexAck.go
+++ b/plc4go/internal/plc4go/bacnetip/readwrite/model/APDUComplexAck.go
@@ -290,7 +290,7 @@ func APDUComplexAckParse(readBuffer utils.ReadBuffer, apduLength uint16) (*APDUC
 		if pullErr := readBuffer.PullContext("serviceAck"); pullErr != nil {
 			return nil, pullErr
 		}
-		_val, _err := BACnetServiceAckParse(readBuffer, uint16(apduLength)-uint16(uint16(uint16(uint16(2))+uint16(uint16(utils.InlineIf(segmentedMessage, func() interface{} { return uint16(uint16(2)) }, func() interface{} { return uint16(uint16(0)) }).(uint16))))))
+		_val, _err := BACnetServiceAckParse(readBuffer, uint16(apduLength)-uint16(uint16(uint16(uint16(3))+uint16(uint16(utils.InlineIf(segmentedMessage, func() interface{} { return uint16(uint16(2)) }, func() interface{} { return uint16(uint16(0)) }).(uint16))))))
 		switch {
 		case errors.Is(_err, utils.ParseAssertError{}) || errors.Is(_err, io.EOF):
 			readBuffer.Reset(currentPos)
diff --git a/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetConstructedDataUnspecified.go b/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetConstructedDataUnspecified.go
index 7c27699ee5d..268a10f2573 100644
--- a/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetConstructedDataUnspecified.go
+++ b/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetConstructedDataUnspecified.go
@@ -112,7 +112,7 @@ func (m *BACnetConstructedDataUnspecified) GetHasData() bool {
 	_ = propertyIdentifier
 	content := m.Content
 	_ = content
-	return bool(bool((len(m.GetData())) == (0)))
+	return bool(bool((len(m.GetData())) != (0)))
 }
 
 ///////////////////////
@@ -213,7 +213,7 @@ func BACnetConstructedDataUnspecifiedParse(readBuffer utils.ReadBuffer, tagNumbe
 	}
 
 	// Virtual field
-	_hasData := bool((len(data)) == (0))
+	_hasData := bool((len(data)) != (0))
 	hasData := bool(_hasData)
 	_ = hasData
 
diff --git a/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetReadAccessProperty.go b/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetReadAccessProperty.go
index 3b0a520bedb..a7c357eb4b5 100644
--- a/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetReadAccessProperty.go
+++ b/plc4go/internal/plc4go/bacnetip/readwrite/model/BACnetReadAccessProperty.go
@@ -144,7 +144,7 @@ func BACnetReadAccessPropertyParse(readBuffer utils.ReadBuffer, objectType BACne
 	if pullErr := readBuffer.PullContext("propertyIdentifier"); pullErr != nil {
 		return nil, pullErr
 	}
-	_propertyIdentifier, _propertyIdentifierErr := BACnetContextTagParse(readBuffer, uint8(uint8(0)), BACnetDataType(BACnetDataType_BACNET_PROPERTY_IDENTIFIER))
+	_propertyIdentifier, _propertyIdentifierErr := BACnetContextTagParse(readBuffer, uint8(uint8(2)), BACnetDataType(BACnetDataType_BACNET_PROPERTY_IDENTIFIER))
 	if _propertyIdentifierErr != nil {
 		return nil, errors.Wrap(_propertyIdentifierErr, "Error parsing 'propertyIdentifier' field")
 	}
@@ -160,7 +160,7 @@ func BACnetReadAccessPropertyParse(readBuffer utils.ReadBuffer, objectType BACne
 		if pullErr := readBuffer.PullContext("arrayIndex"); pullErr != nil {
 			return nil, pullErr
 		}
-		_val, _err := BACnetContextTagParse(readBuffer, uint8(1), BACnetDataType_UNSIGNED_INTEGER)
+		_val, _err := BACnetContextTagParse(readBuffer, uint8(3), BACnetDataType_UNSIGNED_INTEGER)
 		switch {
 		case errors.Is(_err, utils.ParseAssertError{}) || errors.Is(_err, io.EOF):
 			readBuffer.Reset(currentPos)
diff --git a/plc4j/drivers/bacnet/src/test/java/org/apache/plc4x/java/bacnetip/ManualBacNetDecoder.java b/plc4j/drivers/bacnet/src/test/java/org/apache/plc4x/java/bacnetip/ManualBacNetDecoder.java
index 7aba82b35fb..2593b888331 100644
--- a/plc4j/drivers/bacnet/src/test/java/org/apache/plc4x/java/bacnetip/ManualBacNetDecoder.java
+++ b/plc4j/drivers/bacnet/src/test/java/org/apache/plc4x/java/bacnetip/ManualBacNetDecoder.java
@@ -26,7 +26,7 @@
 public class ManualBacNetDecoder {
 
     public static void main(String[] args) throws Exception {
-        final byte[] bytes = Hex.decodeHex("810a002b01040205790109011c020000142c000002f93a06b24e09552e44434a00002f096f2e8204002f4f");
+        final byte[] bytes = Hex.decodeHex("810a001b010030030e0c020000011e294c39014ec4020000014f1f");
         ReadBuffer readBuffer = new ReadBufferByteBased(bytes);
         final BVLC packet = BVLC.staticParse(readBuffer);
         System.out.println(packet);
diff --git a/protocols/bacnetip/src/main/resources/protocols/bacnetip/bacnetip.mspec b/protocols/bacnetip/src/main/resources/protocols/bacnetip/bacnetip.mspec
index a3d40bcdb4c..eefac12b1c9 100644
--- a/protocols/bacnetip/src/main/resources/protocols/bacnetip/bacnetip.mspec
+++ b/protocols/bacnetip/src/main/resources/protocols/bacnetip/bacnetip.mspec
@@ -213,7 +213,7 @@
             [simple   uint 8    originalInvokeId                        ]
             [optional uint 8    sequenceNumber     'segmentedMessage'   ]
             [optional uint 8    proposedWindowSize 'segmentedMessage'   ]
-            [optional BACnetServiceAck('apduLength - (2 + (segmentedMessage ? 2 : 0))')
+            [optional BACnetServiceAck('apduLength - (3 + (segmentedMessage ? 2 : 0))')
                                 serviceAck         '!segmentedMessage'  ]
             // TODO: maybe we should put this in the discriminated types below
             [optional uint 8    segmentServiceChoice 'segmentedMessage && sequenceNumber != 0']
@@ -639,9 +639,9 @@
 ]
 
 [type BACnetReadAccessProperty(BACnetObjectType objectType)
-    [simple     BACnetContextTagPropertyIdentifier('0', 'BACnetDataType.BACNET_PROPERTY_IDENTIFIER')
+    [simple     BACnetContextTagPropertyIdentifier('2', 'BACnetDataType.BACNET_PROPERTY_IDENTIFIER')
                     propertyIdentifier              ]
-    [optional   BACnetContextTagUnsignedInteger('1', 'BACnetDataType.UNSIGNED_INTEGER')
+    [optional   BACnetContextTagUnsignedInteger('3', 'BACnetDataType.UNSIGNED_INTEGER')
                     arrayIndex                      ]
     [optional   BACnetConstructedData('4', 'objectType', 'propertyIdentifier')
                     propertyValue                   ]
@@ -1576,7 +1576,7 @@
                                 data
                             terminated
                             'STATIC_CALL("isBACnetConstructedDataClosingTag", readBuffer, false, tagNumber)'    ]
-            [virtual    bit     hasData 'COUNT(data) == 0']
+            [virtual    bit     hasData 'COUNT(data) != 0']
             [optional       BACnetContextTagPropertyIdentifier('0', 'BACnetDataType.BACNET_PROPERTY_IDENTIFIER')
                             propertyIdentifier
                             'hasData'                                                                           ]