Emerson 848T Function Block Scheduling

Reference Manual
00809-0100-4697, Rev EA
October 2011
Rosemount 848T
C-8
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 ma cr ocycle 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
correspon din g da ta transfer s 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