APPS: Alarm and DIO Control

[The AList]

------------ Forwarded Message ------------
From: Michael Griffin
To: AUTOMATION at CONTROL.COM
Subject: Re: APPS: Alarm and DIO Control

Some slave devices do automatically turn outputs on or off according to 
whether an input is within set limits. That has nothing to do with the Modbus 
protocol however. Modbus is  a communications protocol. It is all about what 
bits go out over the communications cable. It has nothing to do with whatever 
else the slave or master can do in their spare time. You will need to go over 
the data sheets and manuals for various manufacturers to find an I/O module 
that does what you want. 


On September 4, 2008, Erik wrote:
> I have been reading the different discussions and I realize that a slave 
device cannot communicate an alarm condition to the master. The master has to 
poll the slave.
> 
> What I want to do is to program an alarm condition to my slave device that 
when the condition is met the slave would set a bit in the alarm register but 
would also set a DIO to high without the interaction of the master. The slave 
would do this all on its own. I want to know if this is a legal operation in 
Modbus protocol.