Siemens SIMATIC S5-90U, Системное руководство

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Onboard Counter Inputs S5-90U/S5-95U
Example: • Counter counts positive edges
• The comparison value is 3
Figure 11-1. Principle of Operation of the Onboard Counter Inputs
Signal state
at counter input
a a a a a a a
a a a a a a a
a a a a a a a
a a a a a a a
a a a a a a a
24 V
a a a a a a a a
a a a a a a a a
a a a a a a a a
a a a a a a a a
Time
Actual counter
status
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
Com-
parison
value
a a a
a a a
a a a
a a a
a a a
3
a a a
a a a
a a a
a a a
2
a a a
a a a
a a a
a a a
a a a
1
a a a a a a a a
a a a a a a a a
a a a a a a a a
a a a a a a a a
a a a a a a a a
Time
a a a a
a a a a
a a a a
a a a a
a a a a
t
1
Counter is reset to "0"
Entry in diagnostic byte and
call of OB3
a a a a
a a a a
a a a a
a a a a
a a a a
t
2
Explanation of Figure 11-1:
• When reaching the comparison value, the counter is immediately reset to "0".
After the reset, the counter can immediately resume the counting of edges. It can thus not miss
any edges.
• The counter is reset during time interval t
1
whereas t
1
interrupt reaction time.
t
1
corresponds to the reciprocal value of the counter frequency limit (see Section 11.6).
• The cause of the interrupt is entered in the diagnostic byte when t
2
has elapsed. OB3 is then
called up. t
2
interrupt reaction time.
• In the example, t
2
is that long that another edge is present before OB3 is called up. This may
be the case if an OB3 is just being processed when the comparison value is reached (see
Section 10.3).
11-2
EWA 4NEB 812 6115-02b