AB7072-B Subnet LED RED + incorrect data

Hi there,

I am trying to control some Condair GS150 Humidifiers through Modbus RTU with my PLC using the AB7072-B Module. However, I seem to be have some transaction problems as the Subnet LED is red, as well as the data that I am seeing is not correct.
I am attaching my configuration file. Is there something that I have done wrong?

Any help would be appreciated. Thank you

lift gate.cfg (16.0 KB)
GS_5.8.1.7 BACnet_Modbus.xlsx (17.9 KB)


Can you get a copy of the logs?

When reviewing the logs do you see any exception codes that occur?


Hi Kevin,

Please see attached logs.

log2.txt (33.7 KB)


You have several timeouts occurring for your transactions. This means that the transaction is being sent from the communicator but it is not getting a response from the Modbus Slave.

Also one of your transactions is getting a exception code of x02.

(02 hex)

Illegal Data Address

The data address received in the query is not an allowable address for the slave. More specifically, the combination of reference number and transfer length is invalid. For a controller with 100 registers, a request with offset 96 and length 4 would succeed, a request with offset 96 and length 5 will generate exception 02.

Your read holding register (03) with a starting register 5 is experiencing the exception code.

Additionally, i see many functions that are not getting responses at all. I would build the configuration function by function to verify all data is getting through.

Hi Kevin,

Is this where I am making the mistake? Am I inputting these correctly?


The issues with the slave interface where it is not responding to commands being sent from the communicator.

I would review the slave and verify that it is configured to respond with all commands.

Thanks Kevin, the humidifier seem to be wired properly and are set up for Modbus control. I am unable to find the root cause of this problem. Is there anything else I can provide you with that might make it easier for you to help me?



Well you have provided me with everything. Did you reconfigure the unit? The communicator is expecting a response from the slave device, but it’s not getting one. The communicator is functioning as intended, as it is sending all the commands you have set up.

Upon reviewing the logs and configuration again. It looks like Node 3 and 4 are not responding. I would check their connection on the PLC. Node 1 and 2 are getting valid responses.


1 Like

Thanks Kevin, yes at that moment, node 3 and 4 were off. But this red light still remains even when all are on. You are right that node 1 and 2 are transmitting data, but I am only able to read it. When I try to send the demand output the humidifier does not receive it. The communicator can see this output but it is not being received by the humidifier. I am totally lost as to why I am unable to write to the humidifier.


When you send the write commands, what does it show in the logs? Do you get an exception code?

Kevin, I finally just got communication to work. I think it was the way the humidifiers take the input. If I was to just put a random value it wouldnt take it. It had to be a specific binary number. Still not sure why exactly, but hey it works so I wont complain. Thank you for all your help and quick responses, I really appreciate it.


I am glad that this issue is resolved!