Rockwell Automation 5720 DriveLogix System - Manual (Page 230)

Publication 20D-UM002C-EN-P - November 2003
12-6 DriveLogix Back-Up on DeviceNet
Developing the DriveLogix
Back-Up Application The DriveLogix back-up is enabled from an RSLogix 5000 user program with
a few simple ladder rungs (or equivalent). The following rungs are used in the
DriveLogix back-up:
• Back-up Heartbeat Configuration Rungs - required
• Reading Back-up State Rung - optional
• Reading Back-up Status - optional
Back-up Heartbeat Configuration Rungs
The first, and most critical, step is to set the back-up “heartbeat” constant in
the DeviceNet scanner. The heartbeat constant enables the back-up feature
and determines the switchover time (2 x heartbeat).
By default, the heartbeat is zero; this default value disables the back-up mode.
Your user program must set the heartbeat to a non-zero value to enable
back-up.
The heartbeat occurs in multiples of 8ms (i.e. 8, 16, 24, etc.). We recommend a
value of 16-48ms for most applications. The recommended heartbeat times
result in switchover times of 32-96ms. However, these times do not include
controller scan delays.
IMPORTANT
If multiples of 8 are not used for the requested
heartbeat, then the DeviceNet scanner uses the next
higher supported heartbeat value that can be read
from the scanner. For example, if you set the
heartbeat to 10, the scanner uses a 16ms heartbeat.