Rockwell-automation Logix5000 Controllers Sequential Function Charts P Manual de usuario descargar pdf (Pagina 40)

Chapter 1 Design a sequential function chart

When the action is not on its last scan (conveyor_start.Q =1), this statement turns on conveyor_state. When

conveyor_state turns on, the conveyor turns on.

On the last scan of the action (conveyor_start.Q =0), this statement turns off conveyor_state. When

conveyor_state turns off, the conveyor turns off.

You can also use a P0 Pulse (Falling Edge) action to clear data (see Use the

programmatic reset option on page 38). This example uses an action to turn on a

conveyor at the start of a step. A different action turns off the conveyor at the end

of the step.

Example

This action turns on the conveyor. When conveyor_state turns on, the conveyor turns on.

Before the SFC leaves the step, the P0 action turns off the conveyor. On the last scan of the step,

conveyor_state turns off. This turns off the conveyor.

Use the automatic reset option

Automatic reset provides a system-defined cleanup of actions (known as postscan)

when they are shut down when any of the following occur.

• transition out of the associated step

• reset of a stored action

• reset of an SFC routine

Postscan is similar to prescan in that most instructions are executed as if they are

FALSE. Some instructions have specific postscan behavior.

• In RLL, OTE instructions are turned off and non-retentive timers are reset.

• In structured text, the destination of a non-retentive assignment "[:=]" is

cleared.

• A JSR instruction invokes its subroutine but parameters are not passed and

the logic in the subroutine is executed in postscan mode.

• An Add-On Instruction executes its logic routine in postscan mode and

then executes its postscan logic in normal mode (if a postscan routine is

configured).

• Any nested SFC (SFC that an action calls as a subroutine) is reset.

40 Rockwell Automation Publication 1756-PM006F-EN-P - October 2014

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Rockwell-automation Logix5000 Controllers Sequential Function Charts P Manual de usuario Pagina 40