Experimental Physics and
Industrial Control System

Zenon Szalata <[email protected]> · Thu, 16 May 2013 11:38:00 -0700

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