Mitsubishi Electric MELSEC-Q Series Programming Manual page 35

Ex.
[SFC system processing time calculation example]
Using the Q25HCPU as an example, the processing time for the SFC system is calculated as shown below, given the
following conditions.
• Designated at initial START
• Number of active blocks: 30 (active blocks at SFC program)
• Number of inactive blocks: 70 (inactive blocks at SFC program)
• Number of nonexistent blocks: 50 (number of blocks between 0 and the max. created block No. which have no SFC
program)
• Number of active steps: 60 (active steps within active blocks)
• Active step transition conditions: 60
• Steps with satisfied transition conditions: 10 (active steps (no HOLD steps) with satisfied transition conditions)
SFC system process time = (14.5  30) + (5.2  70) + (1.8  50)+ (10.6  60) + (4.3  60) + (56.2  10) + 46.6 =
2391.6s  2.40ms
In this case, calculation using the equation shown above results in an SFC system processing time of 2.40ms.
The scan time is the total of the following times: SFC system processing time, main sequence program processing time,
processing time of transition conditions associated with SFC's active steps, and CPU module's END processing time.
The number of active steps, the number of transition conditions, and the number of steps with satisfied transition conditions
varies according to the conditions shown below.
• When transition condition is unsatisfied
• When transition condition is satisfied (without continuous transition)
• When transition condition is satisfied (with continuous transition)
The method for determining the number of the above items is illustrated in the SFC diagram below.
The following table indicates the number of active steps, number of active transitions, and number of transition condition-
satisfied steps when Step 2 and Step 6 are active.
Whether Transition Presence/Absence of
Conditions Are Satisfied Continuous
or Not Transition

Transition conditions not
satisfied
• Transition conditions 2, 5 Absence
satisfied
Presence
• Transition conditions 3, 6 not
satisfied
Transition conditions 2, 3, 5, 6 Absence
satisfied
Presence
Number of Active Steps Number of Active
Transitions
2 (Steps 2, 6) 2 (Transition conditions 2, 5)
2 (Steps 2, 6) 2 (Transition conditions 2, 5)
4 (Steps 2, 3, 6, 7) 4 (Transition conditions 2, 3, 5, 6)
2 (Steps 2, 6) 2 (Transition conditions 2, 5)
6 (Steps 2 to 4, 6 to 8) 6 (Transition conditions 2 to 7)
Number of Transition
Condition-Satisfied
Steps
0
2 (Steps 2, 6)
2 (Steps 2, 6)
2 (Steps 2, 6)
4 (Steps 2, 3, 6, 7)
3 SPECIFICATIONS
33
3.3 Processing Time
3