modbus Data Unit vs Command

[blakelock]

Howdy all,

I'm attempting to setup communications between a pc and a Yokogawa UT150 furnace controller via modbus over RS-485.  I've found the "NI modbus.llb" and have read up a bit on the forum.  So far I have 2 questions.

1. I'm confused about the difference between the "Modbus Data Unit" and "Modbus Command" that are found in the vi's.  I would like to write a value into a particular D register so which one should I use?  and for that matter, what are the meanings of the items in the "Modbus Command" bundle (i.e. "quantity", "data", and "discrete")?

2.  Also, I'm a little overwhelmed by the dozen or so vi's inlcluded in "NI modbus.llb".  Which one would provide the simplest starting point for sending simple commands to a single instrument?

Any help appreciated.
Blake

[Albert.Geven]

duplicate post