configuring the MODBUS plug-in is a bit tricky. The reason: there are some devices out
there that work with wrong byte order (according to MODBUS specification) and some that
use wrong address offsets (and some that do both wrong). So when you configure a plug-in
for your device you in most cases will not have exact specification of this devices
behaviour, so you only can try all variants: invert/non-invert address/data byteorder,
start with an address counting from 0/1.
I've had more success with version 3.3.2, in that version I am
able to send
the state of four buttons to the device as a "holding register" and read the
Earlier versions did not have all the configuration options but the newer ones should be
backwards-compatible, so the default configuration when adding an plug-in newly should be
a good starting point for you.
When the modbus block reads a state it appears to only outputs a
the state changes. This would appear to mean that if a register's state
remains constant the value never propagates. It ought to be propagated at
least once on the first poll.
This is correct and is the default behaviour of OpenAPC projects, you don't have an
continuous flow of (same) data, you only get new (means changed) data.