Experimental Physics and
Industrial Control System

Hi Zen,

This is my first post to this tech-talk. I was surprised to see that the Beckhoff hides much of its useful memory.

Have you tried a RIO? I recently used one and the whole array table is read/write via modbus and all operations are done in one modbus packet. I even wrote some embedded code to store some interesting data in the array so I could get at it via the modbus front end. Here's the one I used: http://www.galilmc.com/products/rio-47xxx.php

-Dan

-------- Original Message --------

Subject:	Modbus
Date:	Thu, 16 May 2013 11:38:00 -0700
From:	Zenon Szalata <[email protected]>
To:	Mark Rivers <[email protected]>, "[email protected]" <[email protected]>

Hi Mark,
I am still working on an IOC to control stepper motors with Beckhoff 
devices (KL2431 and KL2541).  I am using your modbus (R2.2) support module.
Beckhoff devices are called bus terminals.  A bus terminal has two types 
of registers.
One is a small set, typically 2 and in the case of the KL25x1 terminals 
3, that one can read from or write to directly.  Let's call them 
visible.  The poll thread in modbus does IO to these registers.
The other type is what I call "internal" or invisible registers. One can 
access these registers via the visible registers only. Hence, multiple 
operations need to be performed on the visible registers to either read 
from or write to an invisible register.
I find that while I am writing to one of the invisible registers, at 
times the periodic reading from the visible registers in the poll 
thread, interferes with the writing process.

I assume that I can control the poll timeout using your 
poll_delay.template record.
So, I am thinking that I need to change the poll timeout for the 
terminal I am trying to write to to "disable" poll reading from the 
terminal.  I use seq records to sequence these read and write operations 
and I could add at the beginning of the sequence a request to set the 
timeout, to let's say 10 seconds, and at the end of the sequence restore 
the original timeout.

Is the thread woken up when a new timeout value is written out to the 
modbus module?
Is there a better way to make sure that the poll reads do not interfere 
with the reading from and writing to the invisible registers?
Thanks Mark,
Zen