Rockwell Automation 2098-DSD-xxx Ultra3000 Digital Servo Drives with DeviceNet - Manual (Page 14)

Publication 2098-RM004A-EN-P – August 2002
1-4 Overview
I/O Messaging and Explicit
Messaging with DeviceNet You can configure and monitor the drive with either I/O Messaging or
Explicit Messaging. I/O messages are for time-critical, control-oriented
data. I/O messages typically are used for moving predefined data
repeatedly with minimum protocol overhead. Explicit Messages
provide multi-purpose, point-to-point communication paths between
two devices. Explicit Messaging typically would not be used to
exchange data periodically since I/O Messages have a higher priority
and lower protocol overhead than Explicit Messages. However,
Explicit Messages have more flexibility by specifying a service to be
performed and a specific address.
Although, you can control the drive by writing to various parameters
using Explicit Messages, you should consider writing to the Assembly
Objects, which buffer the I/O data. Then the drive can be configured
to fault if a network communication fault or idle condition occurs.
However, you will have to periodically update the Assembly Object to
prevent the Explicit Messaging connection from closing. Refer to
Using Explicit Messaging to Control the Ultra3000 on page 2-44.
If you write to a parameter using an Explicit Message, the parameter
value will be saved as a working value and in nonvolatile memory.
However, if you write to a parameter using an I/O message, you can
specify whether the parameter value should be saved in nonvolatile
memory or not. Therefore, if a parameter value has to be modified
repeatedly, then you should use I/O messaging and not save the
parameter value to nonvolatile memory because the nonvolatile
memory has a limited number of writes.
ATTENTION
!
The nonvolatile memory has a limited number of
write cycles. Do not save parameter values to
nonvolatile memory (NVMEM) unless absolutely
necessary. In other words, minimize the number of
times parameter values are saved to nonvolatile
memory (NVMEM).