Message sent from AS to Modbus device after online status is restored

Message sent from AS to Modbus device after online status is restored


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


Building Operation 1.5.x to 2.0.3


A feature was added in release 1.5 that is intended to read the devices 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 are unable to handle this message and stop communicating with the AS or ES.


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.

Device indentification.JPG

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 of the device polling:

  1. Open Properties
  2. Set "Poll interval" to "Inhibit"

The trade-off with this work-around is that the online detection for the device is turned off, so the device will never go offline in Building Operation.

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