Tuesday, April 13, 2010

Ladder Logic of Allen Bradley SLC 500





Programming language that is used to control Allen Bradley SLC-500 system known as ladder logic. There are three basic elements associated with the organization ladder logic:
• Rungs
• Instructions
• Branches

RUNGS
Ladder logic instructions written in a rung. During the scanning process, the processor scan from left to right, one by one ladder from the top down.

Key Point of Rungs:
• Rungs scanned from 0 to the highest rung number (top to bottom).
• Rungs read from left to right.
• New Ladder will be given numbers automatically, according to where the ladder is placed in a ladder logic file.
• The last rung in a ladder logic file automatically contains an END instruction.

INSTRUCTIONS
Ladder Logic Instruction is divided into 2 parts:

• Input instructions:
Displayed on the left side of the ladder. Check, comparison, or the specific conditions.

• Output instructions:
Published on the right side.

The key point about the instructions:
• Added instructions displayed on the left side of the rungs while the output instructions are always displayed on the right side of the rungs.

• A rung does not require any input instructions, but must contain at least one output instruction.

BRANCHES
Branches used in ladder logic to create different paths that directly read the state of inputs and outputs.

Bit instructions.
Bit instructions are instructions that ladder logic instructions execute or change a single bit of data table files. Here are three types of bit instructions:
Conditional input instructions.
Non-retentive output instructions.
Retentive output bit instructions.



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