Rockwell Automation 1769-SDN Compact I/O DeviceNet Scanner Module User Manual - Manual (Page 75)

Publication 1769-UM009E-EN-P - August 2009 75
Manually Configure the DeviceNet Network Chapter 5
Expected Packet Rate (EPR)
When the scanner module opens a polled or strobed I/O connection, it sets a
maximum timeout (expected packet rate) with the device. If the device does
not receive a packet from the scanner module within four times the EPR value,
the slave device drops the connection. If the scanner module does not receive
a packet from the slave within four times the EPR value, it drops the
connection and periodically attempts to open a new connection.
When a connection is dropped, status bits in the scanner module identify that
the slave is not online. Slave behavior when a connection is dropped is a
function of the slave device. If the slave is an I/O device, the outputs will be
cleared, held at last state, or set to a fault condition (refer to the slave device’s
documentation for actual I/O behavior when a connection is dropped).
The EPR default value is 75 ms.
Transmit Retries
Transmit Retries specifies the number of times the scanner module attempts to
retransmit a change of state or cyclic message that has not been acknowledged
by the slave device. The connection is not necessarily dropped as a result of
reaching the retry limit.
IMPORTANT
Changing the EPR number should be done carefully because it
effects how long it takes the scanner module to detect a
missing device.