Questions And Answers About Stage Programming - Automation Direct DL05 User Manual

Questions and Answers about Stage Programming

We include the following commonly-asked questions about Stage Programming as an aid to
new students. All question topics are covered in more detail in this chapter.
Q. What does stage programming do that I can't do with regular RLL programs?
A. Stages allow you to identify all the states of your process before you begin programming.
This approach is more organized, because you divide up a ladder program into sections. As
stages, these program sections are active only when they are actually needed by the process.
Most processes can be organized into a sequence of stages, connected by event-based
transitions.
Q. What are Stage Bits?
A. A stage bit is just a single bit in the CPU's image register, representing the active/inactive
status of the stage in real time. For example, the bit for Stage 0 is referenced as "S0". If S0
= 0, then the ladder rungs in Stage 0 are bypassed (not executed) on each CPU scan. If S0
= 1, then the ladder rungs in Stage 0 are executed on each CPU scan. Stage bits, when used
as contacts, allow one part of your program to monitor another part by detecting stage
active/inactive status.
Q. How does a stage become active?
A. There are three ways:
• If the Stage is an initial stage (ISG), it is automatically active at powerup.
• Another stage can execute a Stage JMP instruction naming this stage, which makes it active upon its
next occurrence in the program.
• A program rung can execute a Set Stage Bit instruction (such as Set S0).
Q. How does a stage become inactive?
A. There are three ways:
• Standard Stages (SG) are automatically inactive at powerup.
• A stage can execute a Stage JMP instruction, resetting its Stage Bit to 0.
• Any rung in the program can execute a Reset Stage Bit instruction (such as Reset S0).
Q. What about the power flow technique of stage transitions?
A. The power flow method of connecting adjacent stages (directly above or below in the
program) actually is the same as the Stage Jump instruction executed in the stage above,
naming the stage below. Power flow transitions are more difficult to edit in DirectSOFT 5,
we list them separately from two preceding questions.
Q. Can I have a stage which is active for only one scan?
A. Yes, but this is not the intended use for a stage. Instead, just make a ladder rung active for
1 scan by including a stage Jump instruction at the bottom of the rung. Then the ladder
will execute on the last scan before its stage jumps to a new one.
Chapter 7: RLL
DL05 Micro PLC User Manual, 6th Edition, Rev. A
Stage Programming
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