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Reference Manual
00809-0100-4697, Rev GA
Appendix C: FOUNDATION Fieldbus Technology
November 2014
FOUNDATION Fieldbus Technology
C.5.5 Function block scheduling
Figure C-6 shows an example of a link schedule. A single iteration of the link-wide schedule is
called the macrocycle. When the system is configured and the function blocks are linked, a
master link-wide schedule is created for the LAS. Each device maintains its portion of the
link-wide schedule, known as the Function Block Schedule. The Function Block Schedule
indicates when the function blocks for the device are to be executed. The scheduled execution
time for each function block is represented as an offset from the beginning of the macrocycle
start time.
Figure C-6. Example Link Schedule Showing Scheduled and Unscheduled Communication
To support synchronization of schedules, periodically Link Scheduling (LS) time is distributed.
The beginning of the macrocycle represents a common starting time for all Function Block
schedules on a link and for the LAS link-wide schedule. This permits function block executions
and their corresponding data transfers to be synchronized in time.
Macrocycle Start Time
Offset from macrocycle start
time = 0 for AI Execution
Device 1
Scheduled
Communication
Sequence Repeats
Macrocycle
Offset from macrocycle start time =
20 for AI Communication
Unscheduled
Communication
Device 2
Offset from macrocycle start
time = 30 for PID Execution
Offset from macrocycle start time =
50 for AO Execution
AI
AI
PID
AO
PID
AO
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