Issue
When a Modbus device comes back online after being offline a message is sent from the Building Operation Server to the Modbus device which looks similar to:
WriteData TX on /dev/tac_comporta: 01 2B 0E 01 00 70 77
ReadData RX on /dev/tac_comporta: 01 AB 01 9E F0
This message can cause the Modbus device to restart or stop responding, is it possible to disable it?
Product Line
EcoStruxure Building Operation
Environment
- Building Operation 1.5.x to 2.0.3
- Modbus Device
- Socomec Power Meters
- Crompton Integra 1221 Power Meter
Cause
A feature was added in release 1.5 that is intended to read the device's identification (0x2B). It works by polling this function code (FC). If the Building Operation server does not get a valid reply to this message, it assumes it is not supported by the device and will not request this again. This is usually not a problem but some Modbus devices, such as those listed in the Environment above, are unable to handle this message and will stop communicating with the AS or ES.
Resolution
In Building Operation 2.0.4 and above the option to enable or disable the device identification request (Function code 2B) has been introduced, allowing the poll interval (and online detection) to be set.
In previous versions this message cannot be disabled, however, if device polling is disabled the device identification request won't be requested, which can be used as a work-around.
To turn off the device polling:
- Open Properties
- Set "Poll interval" to "Inhibit"
The trade-off with this workaround is that the online detection for the device is turned off, so the device will never go offline in Building Operation.
In some instances, the third-party Modbus device will need to be restarted to allow communication to resume.
