Rockwell-automation 1772-LV Mini-PLC - 2/15 Programmable Controller (S Manual de usuario descargar pdf (Pagina 58)

Chapter

61

Advanced Instruction Set

This chapter describes advanced programming techniques common to the

controller. In this chapter you will read sections A through E concerning:

Scan Theory

Program Control Instructions

Jump Instructions and Subroutine Programming

Advance Data Manipulation

Block Transfer Instructions

Section A

Scan Theory

In this section you will read:

Scan Function

Scan Time

Scan

Function

In order for the processor to implement your program, it must evaluate the

action that it takes based on monitoring the status of input conditions. In

addition, it must control the status of output devices in accordance with the

program logic. Every instruction in your program requires an execution time.

Execution times vary greatly depending upon the instruction, the amount of data

to be operated on, and whether the instruction is true or false.

As a review from chapter 2, there are two types of scan functions (Figure 6.1):

I/O scan

Program scan

Upon power up, the CPU begins the scan sequence with the I/O scan. During

the I/O scan, data from input modules is transferred to the input image table.

Data from output image table is transferred to the output modules.

Objectives

Introduction

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Rockwell-automation 1772-LV Mini-PLC - 2/15 Programmable Controller (S Manual de usuario Pagina 58