Chelsea will send some code to show how the registers are encoded in Modbus registers.
In Bacnet you can read the priority array which would make things easier for you. When the hand-off-auto switches are active the priority array will show some values at priority level 7 and when the switch is in auto they will show a null value (255).
https://forums.temcocontrols.com/t/controlling-from-external-masters-using-priority-array/441
