Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manual de usuario descargar pdf (Pagina 108)

Publication 1794-UM001G-EN-P - January 2007

108 FlexLogix Back-Up on DeviceNet

Developing the FlexLogix

Back-Up Application

The FlexLogix 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 FlexLogix 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.

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Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manual de usuario Pagina 108