Rockwell Automation 1203-GK5 DeviceNet Communications Module FRN 1.xxx-3.xxx - Manual (Page 79)

Using DeviceNet Explicit Messages 6-11
Using Messages to Control
SCANport Products Explicit messages provide multi-purpose, point-to-point
communication paths between two devices. It is possible to control
SCANport devices through explicit messaging on DeviceNet by
following particular guidelines and by writing to various register
objects that are buffering the I/O data. The write function is protected
to ensure save operation. The guidelines are as follows:
• The adapter cannot be allocated by a master/scanner in order to
allow explicit writes to the register object.
• Write access to any register object within the adapter will not be
allowed if the message is passed through a connection whose
expected packet rate (EPR) is zero.
• The adapter is required to mark any explicit connection after
allowing a write to a register object through it.
• If a marked explicit connection times out based on the EPR, then
the I/O fault action will be that configured for Communication
Loss over the I/O connection.
• If a marked explicit connection is deleted, then the I/O fault
action will be that configured for Idle over the I/O connection.
• Multiple explicit connections can write/overwrite the control I/O
if they meet the guidelines specified. Each connection will need
to be marked individually within the adapter.
• If the adapter gets allocated/re-allocated by a controller such that
valid I/O data is being sent to the adapter, or if an Idle condition
from the allocating controller is transitioned back to valid data,
then all marked explicit connections will be reset to unmarked
and future writes blocked.
• If a marked connection has its EPR value reset to zero (0) after
being marked, then the connection will become unmarked.