Hysteresisofthe Lnterruptvalue - Siemens SIMATIC S5 IP 281 Equipment Manual

R 11/92
Hysteresis of the Interrupt Value
4.6
Each counter is equipped with an interrupt register in which an interrupt can be stored. Accep-
tance of the interrupt value can be triggered by the S5 (+ section 3.4) or by operating mode TCAR
(-t section 6.4.2).
The interrupt value is always compared with the current counter value (hardware comparator).
The following can occur when the counting value reaches the interrupt value.
– An interrupt is triggered (-+ section 4.4).
– The digital output is activated (+ section 6.7).
– Counter 2 is started (+ section 6.4.5, SC2A).
Hysteresis for
When the encoder stops at the interrupt–triggering position, the encoder
interrupt
can oscillate back and forth around this interrupt point. Interrupts would
processing
be triggered continuously or the digital output activated.
To prevent this undesired triggering of interrupts, the interrupt values are
provided with a hysteresis of Al.
The counter cannot trigger a new interrupt unless it reaches a value at least
2 greater or 2 less than the interrupt value.
Example:
– An interrupt is triggered when the value 4000 is reached.
– If the counter oscillates between 3FFFand 4001, no further interrupts are
triggered even if the counter repeatedly reaches the value 4000.
– Anew interrupt is triggered when the counter reaches the value3FFE (or
less) or the value 4002 (or greater) and then assumes the value 4000
again.
The hysteresis is reset by loading the counter or the interrupt register.
AG 1992, Order No:6ES5998-0KP21
4000
t
Hysteresis Interrupt value = 4000
Interrupt Processing
4001 4002 4003
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