Topic: DMD0501

SG - Stage

The Stage (SG) instruction marks the beginning of a stage in a Program code block.

Note: The Stage (SG) instruction is a 'power-rail' instruction. And while all of the Stage instructions are displayed in the left-most column of the ladder diagram (the power rail), they are created in the right-most column of the ladder logic diagram (the output column). This makes creating Stage instructions in Do-more Designer a bit counter-intuitive because the first step is to position the edit cursor in the output column of the ladder logic diagram (the far right) instead of positioning it against the power rail (the far left).

Any time that a Stage is disabled, for example, by a Jump To Stage (JMP), an Indexed Jump (JMPI), a Disable Stage (SGRST), or a Disable Range of Stages (SGRSTR) instruction, the following actions will occur:

• All output coils (OUT) within that Stage will be turned off
   

• All Timers within that Stage will be reset
   

• Edge triggered contacts will be turned off
   

• Edge triggered instructions will be reset

Rising-edge triggered contacts will energize and edge-triggered inputs on instructions that have them will be ON during the first scan of the ladder logic in a Stage if they are ON when the Stage is first enabled..

Note: All Stage programming instructions must be entered in a Program code block; Stage instructions cannot be placed in a Task code block.

For a complete discussion on Stage Programming concepts and how to use the Stage programming instructions effectively, refer to the Help Topic on Stage Programming Concepts.

Parameters:

Note: Use the F9 key (Element Browser) or Down-Arrow key (Auto-Complete) at any time to see a complete list of the memory locations that are valid in the current field of the instruction.

Stage - designates the reference number of the Stage to create. The Stage reference can be entered using its fully qualified name - for example MyProgram.S0 through MyProgram.S127 - or simply its Stage number - for example S0 through S127.

Note: Stage programming instructions can only reference Stages in the same Program code block, they cannot reference Stages in a different Program code block.

The first SG instruction in a Program code block, regardless of its reference number, will automatically become the "Initial Stage". It will be visually recognizable as an Initial Stage because it will have a double border.

Whenever a Program code block is first enabled to run, the Initial Stage will automatically be enabled and all other stages will be disabled. After the first scan of the Program code block the Initial Stage will operate like any other stage in the Program code block.

Status Display:

The Status display of the Stage instruction will indicate the ON/OFF condition of the Stage bit, and if ON, the entire box will be highlighted.

See also:

Stage Instructions in the Do-more Controller

• JMP - Jump To Stage

• JMPI - Indexed Jump
   

• SG - Stage
   

• SGRST - Disable Stage

• SGRSTR - Disable Range of Stages

• SGSET - Enable Stage
   

• SGDIVRG - Jump to Multiple Stages

• SGCONVRG - Converge Multiple Stages to SG

Related Topics:

Stage Programming Concepts

Introduction

Example 1 - A Simple 2-State Process

Stage Transition Instructions

Example 2 - A Lamp On/Off Controller

Example 3 - A Garage Door Opener

Review - Steps to Writing Successful Stage Programs

Example:

Description of a Typical Stage Diagram:

To the right is a stage diagram of a simple sequence control that would fill a vessel, stir its contents and then drain. It is good to imagine the sequence before actually writing the ladder logic.

Initially stage 'Start'  waits for StartSwitch to come ON. When StartSwitch comes ON, the process transitions to stage 'Fill'.

Stage 'Fill' fills the vessel. Once the vessel is full (VesselFull = ON), the process transitions to stage 'Stir'.

Stage 'Stir' stirs for a period of time. Once the time to stir is complete (TimerDone = ON), the process transitions to stage 'Drain'.

Stage 'Drain' empties the contents of the vessel. Once it is decided the vessel is drained, the StartSwitch is flipped OFF and the job is done.

Ladder Logic for the above Stage Diagram:

To the right is a ladder logic equivalent to the above stage diagram.

Once the Program code block containing this stage is first enabled to run, the initial stage 'Start' will be enabled because it is the initial stage (designated by the double border). None of the ladder logic in other stages ('Fill', 'Stir', 'Drain', 'Stop') is executed; only Rung 2. Once StartSwitch comes ON the JMP (Jump To Stage) instruction is executed. This instruction disables stage 'Start', and enables stage 'Fill' so that only the ladder logic in stage 'Fill' is being executed (i.e. Rungs 4-5).

Once stage 'Fill' is enabled Pump turns ON to power the pump motor so that product will begin to fill the vessel. Once the level detector input, VesselFull comes ON, the JMP instruction is executed. This instruction disables stage 'Fill' and enables stage 'Stir'. Also, since stage 'Fill' is now disabled, all of the OUT coils in that stage will be turned OFF (i.e. Pump will go OFF).

Once stage 'Stir' is enabled StirPaddle turns ON to power the stir-paddle motor so that the product can be stirred. Also TMR (StirTimer) begins to time. After 15 minutes of stir time, TimerDone bit comes ON which will execute the JMP instruction. This instruction disables stage 'Stir' and enables stage 'Drain'. Also, since stage 'Stir' is now disabled, all the OUT coils in that stage will be turned OFF and all the timers will be reset.

Once stage 'Drain' is enabled DrainValve turns ON to open the valve for the product to drain out of the vessel. Once StartSwitch turns OFF the JMP instruction is executed. This instruction disables stage 'Drain' and enables stage 'Stop'. Since stage 'Drain' is now disabled, all OUT coils in that stage will be turned OFF.

Once stage 'Stop' is enabled the EXIT instruction is executed and the Program code block containing this stage is exited.

If this sequence need be repeated, then the Program code block containing this stage would have to be run again.

It is possible, however, that instead of exiting the Program code block, the JMP instruction in stage 'Stop' could merely jump back to stage 'Start' using a JMP instruction instead of an EXIT. In this manner the stage would repeat indefinitely as long as the Program code block is not halted.