Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 58)

Chapter
6
6Ć1
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