Publication 1763-RM001C-EN-P - October 2009
Protocol Configuration 509
stations to an operator interface connected to the master station for
monitoring, alarming and logging purposes, and to precondition MSG
instructions to each particular slave.
This second use is based on the supposition that if a slave station did not
respond the last time it was polled, it may not be able to receive and
respond to a MSG instruction now, and so it would most likely process
the maximum number of retries and time-outs before completing in error.
This slows down both the poll scan and any other messaging going on.
Using this technique, the minimum time to message to every responding
slave station actually decreases as the number of slave stations that can’t
respond increases.
About Polled Report-by-Exception
Polled report-by-exception lets a slave station initiate data transfer to its
master station, freeing the master station from having to constantly read
blocks of data from each slave station to determine if any slave input or
data changes have occurred. Instead, through user programming, the
slave station monitors its own inputs for a change of state or data, which
triggers a block of data to be written to the master station when the
master station polls the slave.
About Slave-to-Slave Messaging
If one slave station has a message to send to another, it simply includes
the destination slave station’s address in the message instruction’s
destination field in place of the master station’s address when responding
to a poll. The master station checks the destination station address in
every packet header it receives from any slave station. If the address does
not match the slave’s own station address, the entire message is
forwarded back onto the telemetry network to the appropriate slave
station, without any further processing.
IMPORTANT
In order to remotely monitor and program the slave
stations over the half-duplex network while the master
station is configured for Standard polling mode, the
programming computer DF1 slave driver (typically
Rockwell Software RSLinx) station address must be
included in the master station poll list.
efesotomasyon.com - Allen Bradley,Rockwell,plc,servo,drive
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