Emerson Control Techniques FM-4 Reference Manual page 164

FM-4 Programming Module Reference Manual
Control Loop
Cyclic Program
User Program
Figure 133: Diagram of User Program and a Cyclic Program
The following two figures are timing diagrams of a cyclic program with different utilization values (showing the effect) and
a user program initiated to run on several tasks.
Control Loop
Cyclic Program
User Program
Figure 134: Diagram of User Programs on Two Tasks and a Cyclic Program
150
Cyclic Program Utilization
set to 40%
T0 T0
Update Rate
Cyclic Update = 3x Update Rate
Cyclic Program Utilization
set to 70%
T0 T1
Update Rate
Cyclic Update = 3x Update Rate
Same as above except Cyclic Program Utilization is set to 40%. In
this scenario, Cyclic Program cannot complete within 3 updates and
so Overrun Error occurs in next update. Need less code in Cyclic
Prog, higher Utilization setting, or Larger Cyclic Update Rate setting
Overrun Error
Control Loop + Cyclic Prog + User Progs on two Tasks. Cyclic
Program Utilization set to 70% means cyclic program is suspended
after 70% of update is reached, then resumed next update
T0 T1 T0 T1