Rockwell Automation 2098-DSD-xxx Ultra3000 Digital Servo Drives with DeviceNet - Manual (Page 60)

Publication 2098-RM004A-EN-P – August 2002
2-44 Programming Reference
Using Explicit Messaging to Control the Ultra3000
Explicit messages provide multi-purpose, point-to-point
communication paths between two devices. It is possible to control
the drive through explicit messaging on DeviceNet by following
particular guidelines and by writing to various Assembly Objects that
are buffering the I/O data. Although it is possible to control the drive
by writing to various parameter objects, you should consider using the
Assembly Objects for controlling the drive. The guidelines are as
follows:
• Write to the various Assembly Objects that are buffering the I/O
data.
• Write access to any Assembly Object is not allowed if the message
is passed through a connection whose expected packet rate (EPR)
is zero or if I/O data is being sent over an I/O messaging
connection.
• The drive marks any explicit connection after allowing a write to an
Assembly Object through the connection.
• If a marked explicit connection times out based on the EPR, then
the fault action will be that configured for Communication Loss
over the I/O connection, Comm Fault Action — Parameter 14.
• If a marked explicit connection is deleted, then the fault action will
be that configured for Idle over the I/O connection, Faulted Logic
Command — Parameter 15.
• Multiple explicit connections can write/overwrite the control I/O if
they meet the guidelines specified. Each connection will be
marked individually within the drive.
• If the drive gets allocated/re-allocated by a controller such that
valid I/O data is being sent to the drive, 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 Expected Packet Rate (EPR) value
reset to zero (0) after being marked, then the connection will
become unmarked.
IMPORTANT
Do not use Explicit Messaging to set parameter
objects that are changed frequently. An Explicit Set
causes an NVMEM write. The nonvolatile memory
has a limited number of write cycles.
Note: Explicit Get commands have no effect on
NVMEM.