Modbus registers for inputs and outputs

We recently purchased a T3 – TB controller and a TSTAT10. We are testing them for our future OEM products. The TStat10 was connected to the T3 via the T3 RS485 Sub (as below):

I have been reading the forums and would like to use the Analog input (IN1) of the Tsta10 in the T3-TB for radiant cooling applications. when checking the registry list of the TSTAT10:

Input 1 in the TSTAT have a MB_REG address of 7484 and ID of 405.

I have tried to write a program in the T3 to set VAR1 = 1.2.MB_REG405 and 1.2.MB_REG7484 and I got zero result (T3 Modbus ID is 1 and TSTAT10 modbus id is 2).

The question is how can I get the MB_REGxx address of a modbus input or output of a slave controller and use it in the master controller ?I mean the xx where can I find that?

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The XX is just the register number for the remote device, the register numbers are there in the table and by the looks of it the value is held in two separate registers so you’d need some math to reconstitute them into a normal value reading. Modbus can be very cumbersome I admit.

It will be easier to integrate using Bacnet, that way you can use a statement like
10 VAR1 = 222AI3
Where 222 is the bacnet instance of the subnet device and AI3 is the third input on that same device. You will need to set the protocol of the subnet to Bacnet for this to work.

I use Bacnet and modbus in similar configurations. All works, just bacnet controllers are slower than controllers on modbus, and you can’t update TSTAT10 (T3OEM in my case) on Bacnet. Just my subjective opinion, because controllers performs different tasks and I haven’t done side by side test. I would use modbus, but i am lazy, so i use Bacnet.