Technical data
SINAUT TD7 software package for the CPU
2.3 Structure of the SINAUT user program
Software
212 System Manual, 07/2009, C79000-G8976-C222-07
2.3.3 Time-driven SINAUT program in a cyclic interrupt OB
Introduction
A time-driven SINAUT program is only needed in a CPU if counted pulse acquisition is used
in the CPU.
The counted pulses are acquired over a normal digital input module. To be able to acquire
the pulses reliably, the digital inputs used must be polled for changes at fixed time intervals.
This time interval is based on the duration of the shortest counted pulse. The minimum
permitted counted pulse duration is 50 ms. The same applies to the length of the pause. The
resulting maximum count frequency is 10 Hz.
The time interval at which the counted pulse should be acquired must be approximately half
of the counted pulse duration, in other words, an interval of approx. 25 ms is used for a 50
ms pulse.
For this time-driven counted pulse acquisition, OB35 must be programmed for an S7-300
CPU and one of the available cyclic interrupt OBs, OB30 to OB38, for an S7-400 CPU.
Although all of the cyclic interrupt OBs have a preset time interval (for example, 100 ms for
OB35), this can be changed in 1 ms steps. For example, a cyclic interrupt OB can be set to
25 ms.
The figure below shows how to change the time interval for a cyclic interrupt OB in the HW
Config Properties dialog for the CPU.
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Figure 2-24 Changing the time interval for cyclic interrupt OB35