Set_MQTT_Settings

Overview

The Set_MQTT_Settings function block configures the PLC MQTT client settings, including:

💡 When are settings applied?

The MQTT configuration is applied upon successful execution of the function block. The settings are sent to the COMMS module and take effect as soon as the module is active on the network.

⚠️ Should the function only be called once?

No special care is required, like a first scan call to apply settings.
The function block is called whenever changes in the settings are detected.

Broker_IP[4]        := (USINT)
Port                := (INT)
User_Name           := (STRING)
Password            := (STRING)
Client_ID           := (STRING)
Keep_Alive          := (UINT)
QoS                 := (SINT)
Publish_Topic       := (STRING)
Subscribe_Topic1    := (STRING)
Subscribe_Topic2    := (STRING)
Subscribe_Topic3    := (STRING)
STS_Done            => (BOOL)
STS_Failed          => (BOOL)
STS_Fault_Code      => (USINT)

Interface

Inputs

Name	Type	Range / Units	Description
Broker_IP	ARRAY[0..3] OF USINT	0-255	MQTT broker IPv4 address (e.g. `[192,168,11,25]`).
Port	INT	1-65535	Broker port (typical: `1883` for MQTT, `8883` for MQTTS).
User_Name	STRING	—	MQTT username (can be empty if broker does not require auth).
Password	STRING	—	MQTT password (can be empty if broker does not require auth).
Client_ID	STRING	—	MQTT Client ID (can be empty if broker allows it).
Keep_Alive	UINT	seconds	MQTT keep-alive interval in seconds (typical: `60`).
QoS	SINT	0-2	Quality of Service: `0` = at most once, `1` = at least once, `2` = exactly once.
Publish_Topic	STRING	—	Topic used for publishing messages.
Subscribe_Topic1	STRING	—	Subscribe topic #1 (optional).
Subscribe_Topic2	STRING	—	Subscribe topic #2 (optional).
Subscribe_Topic3	STRING	—	Subscribe topic #3 (optional).

Outputs

Name	Type	Range / Units	Description
STS_Done	BOOL	0 / 1	`TRUE` when all configuration data has been successfully sent to the module.
STS_Failed	BOOL	0 / 1	`TRUE` if the configuration data write operation failed.
STS_Fault_Code	USINT	`#`	Diagnostic code indicating the reason for failure.

Status Codes

Code	Meaning	Description
90	Invalid Broker IP	`Broker_IP` is not a valid IPv4 address (e.g. `0.0.0.0` / `255.255.255.255`).
91	Invalid Port	`Port` is outside the valid range (1..65535).
92	Invalid QoS	`QoS` is outside the valid range (0..2).
96	Unknown error	Unknown error occurred during operation.
97	Module Faulted	The COMMS module is present but not active (faulted / not responding).
98	Module mismatch	Slot 1 is populated but not a COMMS module.
99	Module not found	COMMS module is not part of the current hardware configuration.

Example

PROGRAM PROG_Set_MQTT_Settings
    VAR
        MqttCfg : SET_MQTT_SETTINGS;

        _Broker_IP : ARRAY [0..3] OF USINT := [192, 168, 11, 25];
        _User      : STRING := 'NewUser';
        _Pass      : STRING := 'NewPassword';
        _ClientID  : STRING := 'PLC_01';

        _PubTopic  : STRING := 'monolitix/pub';
        _Sub1      : STRING := 'monolitix/sub1';
        _Sub2      : STRING := 'monolitix/sub2';
        _Sub3      : STRING := 'monolitix/sub3';
    END_VAR

    MqttCfg(
        Broker_IP        := _Broker_IP,
        Port             := 1883,
        User_Name        := _User,
        Password         := _Pass,
        Client_ID        := _ClientID,
        Keep_Alive       := 60,
        QoS              := 0,
        Publish_Topic    := _PubTopic,
        Subscribe_Topic1 := _Sub1,
        Subscribe_Topic2 := _Sub2,
        Subscribe_Topic3 := _Sub3
    );
END_PROGRAM

CONFIGURATION Config0
    RESOURCE Res0 ON PLC
        TASK task1_20ms(INTERVAL := T#20ms, PRIORITY := 1);
        PROGRAM Prog_Instance_SET_MQTT_SETTINGS WITH task1_20ms : PROG_Set_MQTT_Settings;
    END_RESOURCE
END_CONFIGURATION