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System Software for S7-300/400 System and Standard Functions - Volume 1/2
A5E00709327-01
1-7
Understanding the Operation of Time-of-Day Interrupt OBs
To start a time-of-day interrupt, you must first set and then activate the interrupt.
The three following start possibilities exist:
• Automatic start of the time-of-day interrupt. This occurs once you have set and
then activated the time-of-day interrupt with STEP 7. The following table shows
the basic possibilities for activating a time-of-day interrupt with STEP 7.
• You set the time-of-day interrupt with STEP 7 and then activate it by calling
SFC30 "ACT-TINT" in your program.
• You set the time-of-day interrupt by calling SFC28 "SET_TINT" and then
activate it by calling SFC30 "ACT_TINT."
Interval Description
Not activated
The time-of-day interrupt is not executed, even when loaded in the CPU. It can
be activated by calling SFC30.
Activated once only
The time-of-day OB is canceled automatically after it runs the one time
specified.
Your program can use SFC28 and SFC30 to reset and reactivate the OB.
Activated periodically
When the time-of-day interrupt occurs, the CPU calculates the next start time
for the time-of-day interrupt based on the current time of day and the period.
The behavior of the time-of-day interrupt when you move the clock forwards or
backwards is described in /234/.
Note
If you configure a time-of-day interrupt in such a way that the corresponding OB is to be
processed once, the DATE_AND_TIME must not be in the past (relative to the real-time
clock of the CPU).
If you configure a time-of-day interrupt in such a way that the corresponding OB is to be
processed periodically, the start DATE_AND_TIME, however, are in the past, then the time-
of-day interrupt will be processed the next time it is due. This is illustrated in the following
figure.
You can disable or delay and re-enable time-of-day interrupts using SFCs 39 to 42.
Preset
start time
Current
time
Preset
interval
Point at which the time-of-day
interrupt OB is first executed.