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Clock-controlled interrupt
Triggering
User interface OB 9
CPU 948 Programming Guide
C79000-G8576-C848-04
• • If you generate a new delayed interrupt, i.e. call OB 153 with
new parameters, a previously set delayed interrupt is cancelled.
A delayed interrupt currently being processed is continued. This
means that only one delayed interrupt is valid at any one time.
• • If a delayed interrupt occurs without the previous one being
completely processed, the new interrupt is discarded. Delayed
interrupts are not checked for collisions!
• • Note the special functions OB 122 and OB 142 with which you
can disable or delay the servicing of delayed interrupts.
The CPU 948 has a battery-backed clock (central back-up via the
power supply of the central controller), which you can set and read out
using the STEP 5 program. This clock allows time-controlled
execution of a program section.
While the delayed interrupt is used for fast events, time-controlled
interrupts are particularly suitable for processing events which occur
once or which occur at longer intervals, e.g. hourly, daily or monthly.
Once the point in time is reached, the system program calls OB 9.
A clock-controlled interrupt (timed job) is generated by calling the
special function organization block OB 151 (refer to Section 6.13).
Once the time set in OB 151 is reached (a time, a date) the timed job is
executed. The system program interrupts the current program
execution and calls OB 9 (program execution level TIMED
INTERRUPTS). Following this, program execution is resumed at the
point at which it was interrupted.
To use the clock-controlled interrupt, "process interrupts via IB 0 =
off" must be set in data block DX 0.
For a clock-controlled interrupt, OB 9 is called as the user interface. In
OB 9, you write a STEP 5 program to be processed when the OB is
called. If OB 9 is not loaded, program execution is not interrupted.
RUN Mode
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