Re: Devicenet Command again
From: pmm (muralipmanohar_at_hotmail.com)
Date: 04/29/04
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Date: 29 Apr 2004 02:10:23 -0700
"Kevin Kramb" <kekramb.invalid@ra.rockwell.com.invalid> wrote in message news:<1090pfbamj8p3da@corp.supernews.com>...
> "pmm" <muralipmanohar@hotmail.com> wrote in message
> news:1f1fe31f.0404262135.7d76e1e8@posting.google.com...
> > Dear all
> > i am implementing a IO slave module .i have 4 output points which are
> > monitored by 4 discrete output point objects .An assembly object has a
> > output instance which shall monitor these 4 Discreteoutput point
> > objects (as i understood from specs).in the specs the attribute of the
> > assembly object is a byte array .I have a doubt that what will be the
> > master command format inorder to invoke this assembly object.will
> > master send the bytes or bits (in a single byte) as the values for the
> > assembly object attribute . i am not able to make out the exact format
> > of the frame sent by the master for a assembly object to set the
> > values for Discreteoutput point objects monitored by it
> > plz correct me if i am doing in a wrong way
> > regards
> > PMM
>
> Typically, a master device communicates with slave devices
> via one of the Predefined Master/Slave Connection set (PMSCS)
> connections such as Strobe, Poll, or COS...
> These are I/O connection in which the meaning of the data is
> implicitly defined by the connection. This is oppossed to
> explicit messaging where the meaining of the data is explicitly
> spelled out within the message itself.
> Since the meaning of the data within the I/O connection is
> implicitly defined, the message is often just the data itself,
> without any extra information. If you want to transfer four
> bytes of data over an I/O connection then the message format
> probably just needs to be those four bytes of data, one right
> after the other. (If you need to transfer more than eight
> bytes within an I/O connection then you must split the data
> accross more than one CAN packet and use the first byte of
> each packet for the fragmentation protocol.)
>
> The CAN connection IDs of the PMSCS connections are predefined
> in the DeviceNet specification.
>
> Typically, you determine at design time the content and format
> of the data your slave will exchange with the master. You
> also determine which PMSCS connection(s) your slave will use.
> The decision on which connection(s) to use depends on the size
> of the data and the manner in which you want the application
> data to be transferred.
> If you want to send 4 bytes of data from the master to the slave
> in a periodic fashion then the Poll connection might be for you.
>
> For the slave's I'm familiar with, an Assembly Object instance
> is used to model the content and format of the data sent via
> each PMSCS connection. Think of the Assembly data as the slave's
> local copy of a connection's data. The slave code is written
> so that when the PMSCS message is received the data is copied
> into the data buffer for the associated Assembly instance. Or
> when a PMSCS message is sent the data is copied from the data
> buffer of the associated Assembly instance. Since the Assembly
> data is a collection of parameters from other Objects, your
> slave code will also copy or somehow link the data to those
> other objects as well.
>
> I apologize if I strayed from your question but I hope this
> helps.
>
> -- Kevin
Hello Mr Kevin
I have read spec couple of times ,bu8t even now i am landing to confusion
thanks for your Message i will read spec again :-)
have a nice day
PMM
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