Siemens Simatic S7 Series Manual page 63

Definition Boxes and.
High-Speed Counters.
Positioning Example.
The.High-Speed.Counter.Definition.(HDEF).instruction.assigns
the.operating.mode.to.a.specific.high-speed.counter.(HSCx)..
The.mode.selection.defines.the.clock,.direction,.start,.and.
reset.functions.of.the.high-speed.counter..High-speed.counters.
can.be.defined.by.the.definition.box.to.operate.in.any.of.the.
2.available.modes..Not.all.counters.can.operate.in.all.of.the.
available.modes,.however..Refer.to.the.S7-200.System.Manual.
for.definitions.available.for.each.counter.
The.High-Speed.Counter.(HSC).instruction.configures.and.
controls.a.specific.high-speed.counter.based.upon.the.state.of.
the.special.HSC.bits..The.N.parameter.specifies.the.high-speed.
counter.number..Each.counter.has.dedicated.inputs.for.clocks,.
direction.control,.reset,.and.start,.where.these.functions.are.
supported..
Positioning.is.one.example.of.an.application.that.may.require.
use.of.a.high-speed.counter..In.the.following.illustration,.two.
PLC.discrete.outputs.(one.for.forward.and.one.for.reverse).
control.a.reversing.motor.starter,.which,.in.turn,.controls.a.
motor.
The.motor.shaft.is.connected.to.an.encoder.and.to.a.positioning.
screw..A.platform.mounted.on.the.positioning.screw.moves.
away.from.position.0.as.the.motor.turns.in.the.forward.direction.
and.towards.position.0.as.the.motor.turns.in.the.reverse.
direction..Pulses.from.the.encoder.are.connected.to.PLC.inputs.
associated.with.a.high.speed.counter.
Encoder Motor
Reversing
Motor Starter
In.this.example,.the.high-speed.counter.is.programmed.to.
move.the.platform.from.position..to.position.6.and.later.to.
return.to.position...These.positions.could.be.associated.with.
manufacturing.operations.performed.on.a.part.mounted.on.the.
platform..
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