Parameter list

Parameters that influence the MQTT Message Queue (FB_IotMqttMessageQueue, FB_IotMqtt5MessageQueue) as well as the dynamic memory used for the MQTT messages (TwinCAT Router memory):

Name	Type	Default value	Description
cMaxSizeOfMqttMessage	UDINT	102400	Maximum size in bytes of an MQTT message that can be collected in the message queue. If the `FB_IotMqttClient` receives an MQTT message that is too large, it will be completely discarded when trying to store it in the `FB_IotMqttMessageQueue`. If the `FB_IotMqtt5Client` receives such an MQTT message, it will first be reduced by all User Properties when it attempts to store it in the `FB_IotMqtt5MessageQueue`. If this is not sufficient, the MQTT message is discarded completely.
cMaxSizeOfMqttMessageQueue	UDINT	1024000	Maximum size in bytes of an entire message queue including all collected MQTT messages. If the `FB_IotMqttClient` receives a new MQTT message that would exceed the maximum size of the message queue, this message is completely discarded when it is attempted to be stored in the `FB_IotMqttMessageQueue`. If the `FB_IotMqtt5Client` receives such an MQTT message, it waits until there is space in the queue to receive this new message.
cMaxEntriesInMqttMessageQueue	UDINT	1000	Maximum number of messages in a message queue.

Name

Type

Default value

Description

cMaxSizeOfMqttMessage

UDINT

102400

Maximum size in bytes of an MQTT message that can be collected in the message queue.

If the FB_IotMqttClient receives an MQTT message that is too large, it will be completely discarded when trying to store it in the FB_IotMqttMessageQueue.

If the FB_IotMqtt5Client receives such an MQTT message, it will first be reduced by all User Properties when it attempts to store it in the FB_IotMqtt5MessageQueue. If this is not sufficient, the MQTT message is discarded completely.

cMaxSizeOfMqttMessageQueue

UDINT

1024000

Maximum size in bytes of an entire message queue including all collected MQTT messages.

If the FB_IotMqttClient receives a new MQTT message that would exceed the maximum size of the message queue, this message is completely discarded when it is attempted to be stored in the FB_IotMqttMessageQueue.

If the FB_IotMqtt5Client receives such an MQTT message, it waits until there is space in the queue to receive this new message.

cMaxEntriesInMqttMessageQueue

UDINT

1000

Maximum number of messages in a message queue.

Parameters that influence the inputs of an MQTT client (FB_IotMqttClient, FB_IotMqtt5Client):

Name	Type	Default value	Description
cSizeOfMqttClientClientId	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the ClientId.
cSizeOfMqttClientHostName	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the host name.
cSizeOfMqttClientTopicPrefix	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the topic prefix.
cSizeOfMqttClientUserName	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the user name.
cSizeOfMqttClientUserPwd	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the user password.
cSizeOfMqttWillTopic	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the Will-Topic.

Parameters that influence the MQTT 5 properties:

Name	Type	Default value	Description
cSizeOfMqtt5ContentType	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the content type.
cSizeOfMqtt5AuthMethod	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the authentication method.
cSizeOfMqtt5AuthData	UDINT	4096	Maximum size in bytes of the authentication data.
cSizeOfMqtt5ServerReference	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the server reference.
cSizeOfMqtt5ReasonString	UDINT	256	Definition of the STRING size in bytes, which specifies the maximum length of the reason string.
cMaxMqtt5UserProps	UINT	20	Maximum number of UserProperties that can be received with an MQTT 5 message or sent with the help of `FB_IotMqtt5UserProperties`. The processing of UserProperties in the PLC real-time task cycle requires a certain amount of time depending on the quantity, which is why it is better to keep it low.