Re: one Devicenet Question please

From: pmm (muralipmanohar_at_hotmail.com)
Date: 05/17/04 

Date: 16 May 2004 21:48:54 -0700

"Kevin Kramb" <kekramb.invalid@ra.rockwell.com.invalid> wrote in message news:<10aeukmnbjgksc8@corp.supernews.com>...
> "pmm" <muralipmanohar@hotmail.com> wrote in message
> news:1f1fe31f.0405142248.51e1c9c7@posting.google.com...
> > "Kevin Kramb" <kekramb.invalid@ra.rockwell.com.invalid> wrote in message
> news:<10a8cghtcb3nu27@corp.supernews.com>...
> > > "pmm" <muralipmanohar@hotmail.com> wrote in message
> > > > I have been working on IO control application. i have a doubt
> > > > regarding POLL IO messages .i have a 4 in and 4 out Devicenet IO
> > > > module . I wanted to implement the Poll support. i am not able to
> > > > decide what will be the data send by the master in the Poll command
> > > > ,so that my Slave module will open the packet and retrieve the info
> > > > and set them appropriately .ie if masterwants to send a command to my
> > > > 4in 4out device in Poll format what it will send in bit datastream (8
> > > > bytes )other than produced and consumed conn Ids
> > > > Please reply and help me to complete my project
> > > > Regards
> > >
> > > The Poll Command message sent from the master to the slave
> > > can contain any amount of data. If your slave device has
> > > four digital outputs then perhaps your plan is for the
> > > master to control these outputs. If that is the case then
> > > I would expect you will send one byte of data in the Poll
> > > Command. Four of the bits in this byte would correspond
> > > to how the four outputs should be driven. The remaining
> > > four bits could be ignored.
> > >
> > > Similarly, the Poll Response message sent from the slave to
> > > the master can also contain any amount of data. But I
> > > expect you only need to send one byte of data in which
> > > four of the bits correspond to the four input values.
> > >
> > > -- Kevin
> >

Dear Mr Kevin
 thanks for the reply
 
> Your slave application should also know that it needs to send
> the Poll Response after receiving the Poll command. It will
> know to get the data from the Assembly instance associated with
> the input data (and/or know to read the actual input values.)
> The Poll Response also has a unique Connection ID predefined by
> the DeviceNet spec.

Yes sir i have read the connection format and i am clear with them
ie master sends a grp2 command with msgID 101 along with slave's MAC
ID
 and slave sends the response in grp1 with massage id 'F' and its MAC
id
and some bunch of data as application data only.I am very much
confused about these 8 data bytes I can code my own logical
analysation but what happens if my device used with other master, how
does he know that 'to set the output he needs to send so and so... and
to get so and so ..' thats what i am worried of

> When I say "know" above, I mean that this can be hard coded into
> your slave application.
>
> > (If as master )I want to send the information of 4 bits to a slave IO
> > device thats okay but for whom? input or output.
>
> I don't understand why the master would consider sending input
> data to the slave. I'm assuming that your slave measures the
> inputs and sends the input data to the master in the Poll Response.
> Inputs are one-way from the slave to the master. Outputs are
> one-way from the master to the slave. Do I misunderstand?

No No ,:-) I placed the question in wrong format sorry
One thing from spec I can say that only master has the authority to
start & initiate the converstion b/w slave and it self ,am I right
here sir ?
if this is the case if master wants to see the status of inputs he
needs to send a command to slave asking for the status of inputs so
what does he send in the data bytes .that is one part of my confusion
.
(I am thinking to send just instance ID only of Input Assembly and no
extra data so that slave thinks that ither instance ID is of Input
instance i need to respond with the input status )is it correct ?

For Output. if master wants to know the current status of output
points what he normally sends in the data part .and if he wants to
change these output status to some other format ie set new values
what does he send .that is the other part of my problem.

 bcos the poll part spec say that application related data in those 8
bytes there is no information regarding what a slave receives as
command to set/get for output ,and what a slave recieves as command to
send the status of its inputs to master

hope I explained my problem properly waiting for your reply
Regards
PMM

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