Combining Non-Contiguous Modbus Reads on PT21A01 via RAK7431

Hey everyone,

I’m currently working with a PT21A01 temperature acquisition module that’s hooked up via a RAK7431 for RS485-to-LoRaWAN conversion. The sensor exposes two registers that I’m interested in:

0x0000 for the temperature value
0x0020 for the PT100 resistance value

Both are read-only and non-contiguous. Naturally, I tried to combine these polling instructions into a single uplink using function code 03 (Read Holding Registers), but the sensor threw back an error (something like “Illegal Data Value”).

My questions are:

Is there any way to merge these two polling requests into a single uplink? Or am I just destined to send two separate requests every time?

Thanks in advance for your help!
Cheers,
Camila Gomez