Mitsubishi Electric MELSEC-Q Series Programming Manual page 120

• The method for using a step transition watchdog timer is shown below.
When SM90 is turned ON in the operation output of the step that performs a time check as shown below, the step transition
watchdog timer starts timing.
If transition condition a is not satisfied within the set time (10s) after SM90 has turned ON, annunciator F1 turns ON.
(However, the SFC program continues operation.)
When transition condition a is satisfied within the set time and SM90 turns OFF, the step transition watchdog timer stops
timing and is reset.
• If the annunciators (F0 to F255) turn ON, the number of detected annunciators that turned ON and the annunciator
numbers are not stored into SD62, SD63 and SD64 to SD79.
• The step transition watchdog timers of the same number can be used at different steps if they do not become active
simultaneously.
Ex.
4 SFC PROGRAM CONFIGURATION
118
4.6 Step Transition Watchdog Timer
As there is no chance that steps 5 and 6 will be concurrently active, the same watchdog timer can be used at both steps.