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PLCs: Siemens

Additional Ladder Diagram Instructions for Siemens PLCs 320

This class describes the bit logic instructions used in a ladder diagram program. Then, it more thoroughly explains compare, math, move, convert, jump, label, word logic, shift, and rotate instructions.

Difficulty Advanced
Format Online
Number of Lessons 17
Language English

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Objectives
Ladder Diagram Programming
Bit Logic Instructions
Positive Edge and Negative Edge Coil Instructions
Positive Edge and Negative Edge Contact and Coil Instructions
Compare Instructions
Compare Instruction Examples
Math Instructions
Calculate Instructions
Move Instructions
Convert Instructions
Program Control Instructions
Word Logic Instructions
Word Logic Instruction Example
Shift and Rotate Instructions
Shift and Rotate Examples
Summary

List basic instruction categories for Siemens PLCs.
Describe bit logic contact and coil instructions that respond to transitional conditions.
Describe the function of compare instructions.
List examples of math instructions.
Describe the function of a calculate instruction.
Describe the operation of EN and ENO parameters.
Describe the function of a move instruction.
List examples of conversions that can be performed with convert instructions.
Describe the function of jump and label instructions.
List examples of word logic instructions.
Describe the function of shift and rotate instructions.

Vocabulary Term

Definition

BCD

Binary Coded Decimal. A binary code in which each group of four consecutive binary bits represents a decimal digit (0 through 9).

Binary Coded Decimal

BCD. A binary code in which each group of four consecutive binary bits represents a decimal digit (0 through 9).

Bit Logic Instructions

A category of Instructions in the LAD programming language that performs logical operations using single bit memory locations.

Boolean Logic

A type of logic that deals with the use of logical functions such as OR, AND, and NOT.

Byte

8 consecutive bits or a data type for 8-bit bit strings.

Coil Instructions

Graphical instructions in a LAD program that control a status bit in the process image.

Contact Instructions

Graphical instructions in a LAD program that control power flow to other instructions.

Data Block

DB. An organized set of data in a Siemens PLC program that is used by one or more program blocks. An instance DB stores data use by one program block. A global data block contains data that is available to any program block.

Data Type

A classification that identifies how data in a memory location is interpreted. There are a variety of data types and they are often represented by shorthand names such as Int for a 16-bit signed integer or Real for 32-bit floating point values.

Data Block. An organized set of data in a Siemens PLC program that is used by one or more program blocks. An instance DB stores data use by one program block. A global data block contains data that is available to any program block.

DInt

Signed Double Integer. A data type for 32-bit signed whole numbers.

Double Word

32 consecutive bits or a data type for 32-bit bit strings.

IEC 61131

A standard of the International Electrotechical Commission that provides common approaches and concepts for PLCs. Part three of the standard describes the LAD programming language for PLCs.

Int

Signed integer. A data type for 16-bit signed whole numbers.

LAD

Ladder diagram programming. A graphical programming language defined in part 3 of the IEC 61131-3 standard.

Ladder Diagram

LAD. Also sometimes referred to as ladder logic. A graphical programming language defined in part 3 of the IEC 61131-3 standard.

Linear Program

A PLC user program with all the instructions in the main program block (OB1).

Negative Edge

A 1 to 0 transition of a bit or the result of logic operation (RLO).

Network

A logical connection of instructions that represents one rung of a LAD program. These instructions are executed from left to right beginning with the instructions closest to the power rail.

OB1

Organization Block 1. The main program block in a Siemens PLC program.

Operand

A part of a PLC instruction that identifies a memory location associated with the instruction.

Organization Block

A type of program block in a Siemens PLC that interfaces the PLC operating system to the user program. Every program must have at least one OB. If it has only one OB, that block is identified as OB1.

Organization Block 1

OB1. The main program block in a Siemens PLC program.

Positive Edge

A 0 to 1 transition of a bit or the result of logic operation (RLO).

Power Flow

A condition in a LAD network for which the result of logic operation to that point in the network is a logic 1

Power Rail

The vertical line on the left in each network of a LAD program.

Program Block

A grouping of PLC instructions. A Siemens PLC can have three types of program blocks: organization blocks (OBs), function blocks (FBs), and functions (FCs).

Real

A data type designation for 32-bit floating point values.

Result of Logic Operation

RLO. The intermediate solution to a configuration of instructions.

RLO

Result of Logic operation. The intermediate solution to a configuration of instructions.

Scan

A repetitive process performed by a PLC CPU that includes updating input status, executing the user program, updating outputs and other important tasks.

Signed Double Integer

DInt. A data type for 32-bit signed whole numbers.

Signed Integer

Int. A data type for 16-bit signed whole numbers.

STEP 7

Software used for the configuration, programming, testing, and diagnosis of Siemens SIMATIC S7 PLCs.

STEP 7 (TIA Portal)

Siemens STEP 7 PLC software within TIA Portal.

Structured Program

A PLC program that divides the user program into multiple program blocks. Depending upon how the program is structured, a specific program block may be executed in each scan of the user program or on a conditional basis.

TIA Portal

Siemens Totally Integrated Automation Portal. Software used for designing, commissioning, operating, maintaining, and upgrading automation systems.

Word

16 consecutive bits or a data type for 16-bit bit strings.