Devicenet POLL doubt

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Dear all

I am implementing Devicenet slave device, in which I want to use a
POLL command but I am stuck with the expected_packet_rate in POLL.
what should be the default value of it .
why should I configure expected_packet_rate in POLL because in POLL
the slave will respond to master command and there is no specific
chance that master will request every time after a specific interval.
master can request at any time asynchronously so what is the need of
using expected_packet_rate in POLL .
is there any specific use of it
kindly explain me
thanks in advance
PMM

Re: Devicenet POLL doubt

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That depends on your application, it is also one of the parameters that the
master can set when it opens the poll link

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The EPR is used to configure the timeout for the connection, if you look at
the DeviceNet specification you will see that the POLL connection must time
out after several (I don't have my spec. here, I can't remember how many)
EPR times, at which point there is a product specific timeout handler, some
sevices switch all outputs off, others set a special output, some set the
outputs to programmable values - depends on the product, but the connection
must be set to a timeout fail state and can't respond to any more POLL
commands until it has been reset.

Stan Katz



Re: Devicenet POLL doubt
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Dear Mr Katz
Thanks for you reply i was in doubt what to place on ouputs after the
time out event .your reply shown me a direction
Thanks again
PMM

Re: Devicenet POLL doubt
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The default value of the expected_packet_rate attribute for
the Poll connection instance (and other I/O connections)
should be zero.  See Table 7.3, "Default Poll Connection
Object attribute values".

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The expected_packet_rate attribute for the Poll connection
must be configurable because the DeviceNet Specification says
so.  "Important: As far as attribute modification is concerned,
Predefined Master/Slave I/O Connections (at a minimum) support
the modification of the expected_packet_rate attribute."

Figure 7.3, "Predefined Master/Slave I/O Connection State
Transition Diagram" shows that setting the expected_packet_rate
is how the connection transitions from the "Configuring" state
to the "Established" state.  This is why the master will set
the expected_packet_rate after allocating the connection.

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Think of it from a different perspective.  Say, for example
that the master establishes the Poll connection with a slave
but then the master goes off-line for some reason.  How can the
slave know that the master is no longer using the connection?
How can the slave know to close the connection so that the
connection can be re-established?

This situation is why the expected_packet_rate is important
to the slave.  If the slave does not receive a message from
the master in four times the expected_packet_rate then it will
close the connection.

The master *does* have to periodically send the Poll request
to the slave in order to keep the connection open.

 -- Kevin



Re: Devicenet POLL doubt
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Dear Mr Kevin
Thanks you the reply
as always you did!!
 you helped me out again :-)
Thanks a lot
PMM

Re: Devicenet POLL doubt
Quoted text here. Click to load it

Dear Mr Kevin
Thank you for the reply
as always you did!!
 you helped me out again :-)
Thanks a lot
PMM

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