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Possible value types of I/O tags: Ci, Co, TxtI, TxtO, Qi, Ci, Co, Ai, Ao, Di, Do, TiR, ToR, TiA, ToA.
The MQTT implementation supports three work modes:
- Text mode: The original implementation of the MQTT protocol contained only input text I/O tags with the addresses IN_TOPIC, IN_DATA, and optionally a pair of I/O tags with the addresses IN_ID and ACK_ID. The first two I/O tags were used to publish the received Topic and Payload (which then needed to be parsed in the script), the second two points were used to publish the packet identifier and confirm the processing of the packet. Thus, it was possible to ensure that for data sent with QoS > QoS_0, confirmation was sent only after data processing in the script.
Output I/O tags with the addresses OUT_TOPIC and OUT_VALUE are used for writing. - JSON mode: An extension for processing Payload with JSON data (Payload Type=JSON) was implemented with the help of input I/O tags with addresses JA=json_address. The D2000 KOM process directly parses the JSON payload and sets the values of I/O tagswith JSON addresses. I/O tags with addresses IN_TOPIC, IN_DATA, IN_ID, and ACK_ID may not exist at all.
Output I/O tags with the addresses OUT_TOPIC and OUT_VALUE are used for writing. - Sparkplug mode: An extension for Payload processing with Sparkplug data (Payload Type=Sparkplug) has been implemented using input I/O tags with addresses SA=sparkplug_address. The D2000 KOM process directly parses the Sparkplug payload and sets the values of I/O tags with the Sparkplug addresses. I/O tags with addresses IN_TOPIC, IN_DATA, IN_ID and ACK_ID may not exist at all.
Writing simple values is possible using output I/O tags with addresses ST=type;SA=sparkplug_address, where type is the Sparkplug definition of a data type (eg Int8, UInt16, DateTime, String, etc).
| Type of I/O tag | Address | Description | ||||||
|---|---|---|---|---|---|---|---|---|
| I/O tags for reading data sent by the MQTT server through a PUBLISH message. Note: values of I/O tags are set by the D2000 KOM process in the order IN_TOPIC, IN_DATA, and IN_ID. It is not necessary for the configuration to contain all three I/O tags. | ||||||||
| TxtI |
| Topic (Topic) of received PUBLISH message. | ||||||
| TxtI |
| Data (Payload) of received PUBLISH message. | ||||||
| Ci |
| Identifier of a packet (Packet Identifier) of PUBLISH message that depends on the level of validation (QoS). For messages sent with QoS_0, the identifier is zero, for QoS_1 and QoS_2, it is a positive 16-bit number. Note: if the MQTT server sends also messages with the QoS_0 level of validation and the ACK_ID I/O tag is configured, then we recommend activating the option New value when changing time in the Filter tab, so that repeated writing of the value 0 will cause a new value that differs only in a timestamp to be generated. | ||||||
| I/O tag to confirm the received data to the MQTT server. | ||||||||
| Co |
| If an output I/O tag with ACK_ID address is defined, the D2000 KOM expects confirmation of the processing of each message by writing a copy of the value of the IN_ID tag. Only after, it sets values from the next received PUBLISH message (if it was received in the meantime) into the IN_TOPIC, IN_DATA, and IN_ID I/O tags (in this order). In the case of the QoS_0 level of confirmation, it is, therefore, necessary to repeatedly set the value of the I/O tag ACK_ID to 0. If the I/O tag ACK_ID does not exist, the values are written into the IN_TOPIC, IN_DATA, and IN_ID I/O tags immediately after the PUBLISH message is received and processed. Note: for the messages received with the QoS_0 level of validation, no confirmation is sent to the MQTT server, only the values of the received PUBLISH message will be published. | ||||||
| I/O tags for sending values to the MQTT server through a PUBLISH message. Note: in order for the D2000 KOM process to send the PUBLISH messages to the MQTT server, both I/O tags must be defined within one station. | ||||||||
| TxtO |
| The topic of the PUBLISH message being sent. | ||||||
| TxtO |
| Data (Payload) of the PUBLISH message being sent. Note: sending the message is performed out as a result of writing to the OUT_VALUE I/O tag (i.e. if the Topic does not change then it is sufficient to set the OUT_TOPIC point once - e.g. by using default value). | ||||||
| I/O tags for parsing JSON messages | ||||||||
TxtI, TxtO, Qi, |
| If Payload Type=JSON, the message is parsed as JSON data. The json_address value specifies the name of the JSON field whose value is to be assigned to the I/O tag. For other examples, see the description of the LoRaWAN protocol's Envelope type I/O tags. | ||||||
| I/O tags for parsing Sparkplug messages | ||||||||
TxtI, TxtO, Qi, |
SA=sparkplug_address Output I/O tags: | If Payload Type=Sparkplug, the message is parsed as Sparkplug data (a binary format built on Google Protocol Buffers). Sparkplug data contains metrics that have text identifiers. The value type must be specified for output I/O tags. Simple types are supported:
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