Specifications

SIMATIC Instructions
9-171
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
Time-Based Interrupts
Time-based interrupts include timed interrupts and the Timer T32/T96 interrupts.
The CPU can support timed interrupts. You can specify actions to be taken on a
cyclic basis using a timed interrupt. The cycle time is set in 1-ms increments from
1 ms to 255 ms. You must write the cycle time in SMB34 for timed interrupt 0, and
in SMB35 for timed interrupt 1.
The timed interrupt event transfers control to the appropriate interrupt routine each
time the timer expires. Typically, you use timed interrupts to control the sampling of
analog inputs at regular intervals or to execute a PID loop at a timed interrupt.
A timed interrupt is enabled and timing begins when you attach an interrupt routine
to a timed interrupt event. During the attachment, the system captures the cycle
time value, so subsequent changes do not affect the cycle time. To change the
cycle time, you must modify the cycle time value, and then re-attach the interrupt
routine to the timed interrupt event. When the re-attachment occurs, the timed
interrupt function clears any accumulated time from the previous attachment, and
begins timing with the new value.
Once enabled, the timed interrupt runs continuously, executing the attached
interrupt routine on each expiration of the specified time interval. If you exit the
RUN mode or detach the timed interrupt, the timed interrupt is disabled. If the
global disable interrupt instruction is executed, timed interrupts continue to occur.
Each occurrence of the timed interrupt is queued (until either interrupts are
enabled, or the queue is full). See Figure 9-66 for an example of using a timed
interrupt.
The timer T32/T96 interrupts allow timely response to the completion of a specified
time interval. These interrupts are only supported for the 1-ms resolution on-delay
(TON) and off-delay (TOF) timers T32 and T96. The T32 and T96 timers otherwise
behave normally. Once the interrupt is enabled, the attached interrupt routine is
executed when the active timer’s current value becomes equal to the preset time
value during the normal 1-ms timer update performed in the CPU. You enable
these interrupts by attaching an interrupt routine to the T32/T96 interrupt events.