Starting and stopping an ABB VFD

[pjmaxx66]

I have a ACS800-U4 ABB drive using a RETA-01 modbusTCP
I can read and write everthing but I am having issues understanding how to read and write the control word bits at 40001.
I am trying to use 2 basicbuttons to start and stop the unit.
I have read everything I can find here and eslewhere but still no clear answer(at least for me).
This is my first attemp at modbus and Advanced HMI, I have managed to get everything else working.
Any insite,help or examples would be awesome.

[Archie]

I see the RETA-01 does not support function code 22 (0x16), which is used for masked bit writing to registers. This explains why your button will not set the bits as expected. There are 2 work arounds. If you only need to set 1 bit at a time in a register, then you can set the OutputType of the BasicButton to WriteValue, then set ValueToWrite to the bit value, for example to set bit 3 use value of 16

The other option is to use code to read the value, "OR" the bit to set, then write that value. There is a risk to this..... if something else changes the register value in between your read and write, then it will not write the correct value.