Schneider Electric 890USE17700 - Manual (Page 156)

Advanced Configuration Features
156 890USE17700 April 2004
What Is a Reflex Action?
Summary Reflex actions are small routines that perform dedicated logical functions directly on
the Advantys island bus. They allow output modules on the island to act on data and
drive field actuators directly, without requiring the intervention of the fieldbus master.
A typical reflex action comprises one or two function blocks that perform:
z Boolean AND or exclusive-OR operations
z
comparisons of an analog input value to user-specified threshold values
z up- or down-counter operations
z timer operations
z the triggering of a latch to hold a digital value high or low
z the triggering of a latch to hold an analog value at a specific value
The island bus optimizes reflex response time by assigning the highest transmission
priority to its reflex actions. Reflex actions take some of the processing workload off
the fieldbus master, and they offer a faster, more efficient use of system bandwidth.
How Reflex
Actions Behave Reflex actions are designed to control outputs independently of the fieldbus master
controller. They may continue to turn outputs on and off even when power is
removed from the fieldbus master. Use prudent design practices when you use
reflex actions in your application.
WARNING
UNEXPECTED OUTPUT OPERATION.
For outputs that are configured to respond to reflex actions, the output
state represented in the island’s network interface module (NIM) may
not represent the actual states of the outputs.
z Turn off field power before you service any equipment connected to
the island.
z
For digital outputs, view the echo register for the module in the
process image to see the actual output state.
z For analog outputs, there is no echo register in the process image.
To view an actual analog output value, connect the analog output
channel to an analog input channel.
Failure to follow this precaution can result in death, serious injury,
or equipment damage.