Rockwell Automation 1788-FFCT NI-FBUS Configurator User Manual - Manual (Page 16)

Publication 1788-UM052B-EN-P - April 2002
1-8 Fieldbus Overview
Schedules
A schedule of data traffic allows communication to be deterministic,
meaning that data is transferred between a given set of devices at the
same time during each loop.
The schedule can be divided into two parts: a function block schedule
that determines when a block executes, and a publishing schedule
that determines when data parameters are published over the fieldbus.
The function block schedule is downloaded to the device that
contains the function blocks, and the publishing schedule is usually
downloaded to a device or devices that have link master capability.
The link master running the publishing schedule, and therefore
controlling the process, is the LAS.
Downloading the schedule to multiple devices with link master
capability ensures that the process is controlled, even if the LAS fails.
If the LAS fails, another device with link master capability takes over
the bus and runs the schedule. Figure 1.8 shows the relationship of
the two schedules to the device, link, link master, and LAS.
Figure 1.8 Publishing and Function Block Schedules Relationships
LAS
(Publishing
Schedule)
Basic Device
(Function Block
Schedule)
Basic Device
(Function Block
Schedule)
Link
Link Master
(Function Block Schedule,
Publishing Schedule)
Linkage
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