I am trying to interface an NI cRIO with an Alycat Mass Flow Control, using Modbus RTU, with the cRIO as the master and the Alicat as the slave. I am able to read registers easy enough (16-bit and 32-bit) however, I am not able to write to any registers. For example: the Alicat Register for writing a value to a gas is #400046. I am able to write to that address from my RedLion HMI, so I am certain it is correct. The Alicat Modbus Manual says it uses "16-bit inter value 40046". Then, I create a Text Ring in the LV and then edit the values so that 0=Air, 1=Argon................etc.. . I am not super experienced with LabVIEW so I am not sure what my next step is. I tried using different data types and word sizes but nothing is working. So, I am using a UINT16. My Modbus settings are over serial (2-wire), mode is RTU, and I have the "Use function code 16 for single write" enabled but it doesn't appear to be working. Would anyone have an idea as to why this is happening? Thank you much for your time.