MVI56E-LDM-MQTT ♦ MQ Telemetry Transport
Configuration File Details
ControlLogix® Platform
Quick Start Guide
ProSoft Technology, Inc.
Page 45 of 55
9.1.2 PLC Path
This defines the connection string to connect to the PLC.
9.1.3 Sync Time with PLC
A flag indicating if the system time should be synchronized with the PLC.
Value
Description
0
Default value. Synchronize once, if current system year is less than 2019, which is usually case
after system restart. This helps prevent a system reset when PLC time is not set.
1
Synchronize one time after the first successful connection to the PLC.
2
Synchronize after every successful connection to the PLC.
9.1.4 Status Print Interval
This setting is optional.
MQTT Broker periodically checks the connection status. Messages are written to the log
system on every status change. Additional status messages are written at the interval
defined in this parameter, whether or not the status has changed.
The Default value is 10 (seconds).
9.1.5 Tags
The following table includes tags that are defined in the PLC with the settings to map
them to MQTT messages:
Parameter
Description
Tag
Name of the tag in PLC. Defined for MVI56E-LDM only.
DataType
Data Type of the tag in the PLC. Possible values are: BOOL, SINT, INT, DINT, LINT, USINT,
UINT, UDINT, ULINT, REAL, LREAL, BYTE, WORD, DWORD, LDWORD, STRING82
ScanRate
Defines how often the tag value is read from the PLC, in milliseconds.
Access
Defines if the tag is read-only (value is RD), or readable and writable (value is RDWR).
Topic
Name of the MQTT topic for which the data values are published.
Subscribe Topic
Optional. Ignored if the
Access
field is set to RD (read only)
The name of the MQTT topic on which MQTT-LDM subscribes to receive messages with
new values written to the PLC for this tag.
If this option is omitted, or has an empty value, the system uses the same topic used for
publishing. In this case, the MQTT-LDM receives its own publish messages as well.
Although the received value is written only if it is different than the last read value, there
is no guarantee that an older value is not written due to race conditions. It is
recommended to use a different Subscribe topic name, rather than a Publish topic name.
In the sample configuration files, the Subscribe topic name is composed by adding
/Set
at the end of the Topic name.
After changing the configuration file, the process
mqtt-ldm-sample-app-mvi56e
must
be re-started.
