Rockwell Automation 5720 DriveLogix System - Manual (Page 87)

Publication 20D-UM002C-EN-P - November 2003
Placing and Configuring Local I/O 4-3
The FlexBus continually scans all the slots (0-7) on the DIN rail. The FlexBus
scans the DIN rail, starting with slot 0, then scanning slot 1, and continuing
with all the slots, and then repeating the cycle. Even if a module is inhibited or
a slot is empty, the FlexBus scans that slot. The FlexBus scan identifies where
modules reside and collects module data for the controller scan.
The controller scans only those modules that are configured in the Control
Organizer. This scan updates the module tags with current data. The RPI for
the DIN rail affects how fast the controller gets data from the FlexBus.
Determining When the
Controller Updates I/O The DriveLogix system follows a producer/consumer model. Input modules
produce data for the system. Controllers, output modules, and intelligent
modules produce and consume data. The producer/consumer model
multicasts data. This means that multiple nodes can consume the same data at
the same time from a single device.
The controller continually scans the control logic. One scan is the time it takes
the controller to execute the logic once. Input data transfers to the controller
and output data transfers to output modules asynchronous to the logic scan.
TIP
If you want data to remain constant throughout one scan,
make a copy of the data at the beginning of the scan and
use the copy throughout the scan.