Page 182 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Introduction to Microprocessors Dinesh Kumar, Lovely Professional University

Notes Unit 13: Subroutines

CONTENTS

Objectives
Introduction
13.1 Subroutine
13.1.1 Definition
13.1.2 Calling a Subroutine
13.1.3 Exiting a Subroutine
13.2 Restart Sequence
13.3 Conditional Call Instruction

13.3.1 Subroutine call
13.3.2 Trap subroutine call activation/deactivation
13.4 Return Instruction
13.5 Summary
13.6 Keywords
13.7 Self-Assessment Questions

13.8 Review Questions
13.9 Further Reading

Objectives

After studying this unit, you will able to understand the following:
• Explain the definition of subroutine

• Describe how to create a subroutine
• Explain the procedure to call a subroutine
• Describe about restart sequence

• Define conditional call instruction and its uses; and
• Explain return instruction

Introduction

A subroutine is a container that holds a series of VBScript statements. Suppose you'd like to
create a block of code that accomplishes some specific task. Maybe you need to accomplish that
task in various places throughout your code. All you need to do is create, or declare, the subroutine
in your script. Once you've declared the subroutine, you can call it anywhere within your code.
When your program calls a subroutine, the flow of the code is temporarily diverted to the
statements within the subroutine.
Once the subroutine has finished executing, control returns to the code that called the subroutine
and execution picks up from there. A subroutine is a block of code that can be called from anywhere
in a program to accomplish a specific task. Subroutines can accept starting data through subroutine

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