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A51 Assembler

A251 Assembler

Macro Assemblers for the 8051

and MCS

251 Microcontrollers

User's Guide 04.95

iiKeil Software Information in this document is subject to change without notice and does not represent a commitment on the part of the manufacturer. The software described in this document is furnished under license agreement or nondisclosure agreement and may be used or copied only in accordance with the terms of the agreement. It is against the law to copy the software on any medium except as specifically allowed in the license or nondisclosure agreement. The purchaser may make one copy of the software for backup purposes. No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or information storage and retrieval systems, for any purpose other than for the purchaser's personal use, without written permission. © Copyright 1988-1995 Keil Elektronik GmbH., and Keil Software, Inc.

All rights reserved.

Keil C51™ and dScope™ are trademarks of Keil Elektronik GmbH.

Microsoft

, MS-DOS , and Windows™ are trademarks or registered trademarks of Microsoft Corporation. IBM , PC , and PS/2 are registered trademarks of International Business

Machines Corporation.

Intel , MCS

51, MCS

251, ASM-51

, and PL/M-51 are registered trademarks of Intel Corporation. Every effort was made to ensure accuracy in this manual and to give appropriate credit to persons, companies, and trademarks referenced herein.

A15 D05/12/95

A51 Assembler / A251 Assembler iii

Preface

This manual describes how to use the A51 and A251 macro assemblers. The A51 and A251 assembler translate programs you write in assembly language into executable machine instructions. You may use the A51 assembler to assemble programs for the 8051 family of microcontrollers. You may use the A251 assembler to assemble programs for the 8051 family as well as the MCS 251 family of microcontrollers. This manual assumes that you are familiar with the MS-DOS operating system and know how to program the 8051 or MCS 251 microcontrollers. This manual is divided into the following chapters. "Chapter 1. Introduction," describes the basics of assembly language programming. "Chapter 2. 8051 and MCS 251 Architecture," contains an overview of the 8051 and MCS 251 hardware. "Chapter 3. Writing Assembly Programs," describes assembler statements, operands and address descriptors, and the rules for arithmetic and logical expressions. "Chapter 4. Assembler Directives," describes how to define segments and symbols and how to use all directives. "Chapter 5. Standard Macros," describes the function of the standard macros and contains information for using standard macros. "Chapter 6. Macro Processing Language," defines and describes the use of the

Intel Macro Processing Language.

"Chapter 7. Invocation and Controls," describes how to invoke the assembler and how to control the assembler operation. "Chapter 8. Error Messages," contains a list of all assembler error messages and describes their causes and how to avoid them. The Appendix includes information on the 8051 and MCS 251 instruction set, a summary of directives and controls, the differences between assembler versions, and other items of interest. ivPreface

Document Conventions

This document uses the following conventions:

ExamplesDescription

README.TXT

Bold capital text is used for the names of executable programs, data files, source files, environment variables, and commands you enter at the MS-DOS command prompt. This text usually represents commands that you must type in literally. For example:

CLS DIR BL51.EXE

Note that you are not required to enter these commands using all capital letters. CourierText in this typeface is used to represent information that displays on screen or prints at the printer. This typeface is also used within the text when discussing or describing command line items. VariablesText in italics represents information that you must provide. For example, projectfile in a syntax string means that you must supply the actual project file name. Occasionally, italics are also used to emphasize words in the text. Elements that repeat...Ellipses (...) are used in examples to indicate an item that may be repeated.

Omitted code

Vertical ellipses are used in source code examples to indicate that a fragment of the program is omitted. For example: void main (void) { while (1); !Optional Items" Optional arguments in command-line and option fields are indicated by double brackets. For example:

C51 TEST.C PRINT !(filename)"

{ opt1 | opt2 }Text contained within braces, separated by a vertical bar represents a group of items from which one must be chosen. The braces enclose all of the choices and the vertical bars separate the choices. One item in the list must be selected. KeysText in this sans serif typeface represents actual keys on the keyboard.

For example, "Press Enter to continue."

A51 Assembler / A251 Assembler v

Contents

Chapter 1. Introduction......................................................................................1

What is an Assembler?..................................................................................................1

How to Develop A Program .........................................................................................2

Advantages of Modular Programming....................................................................2

Efficient Program Development..............................................................................3

Multiple Use of Subprograms.................................................................................3

Ease of Debugging and Modifying..........................................................................3

Modular Program Development Process ......................................................................3

Segments, Modules, and Programs .........................................................................4

Program Entry and Exit...........................................................................................4

Relocation and Linkage...........................................................................................5

Keeping Track of Files............................................................................................5

Writing and Assembling Programs...............................................................................6

Chapter 2. 8051 and MCS 251 Architecture ....................................................9

New Features of the MCS 251 Architecture.................................................................9

8051 and MCS 251 Memory Model...........................................................................10

8051 Address Space..............................................................................................11

Program Memory..................................................................................................12

Internal Data Memory...........................................................................................12

External Memory ..................................................................................................12

Memory Classes....................................................................................................13

8051 and MCS 251 Register File................................................................................14

Special Function Registers....................................................................................16

Differences to the 8051...............................................................................................16

8051 Compatibility ...............................................................................................17

Timing Issues........................................................................................................17

Stack Pointer (SPX)..............................................................................................17

Program Status Word............................................................................................17

PSW Bit Definitions..............................................................................................18

Chapter 3. Writing Assembly Programs ........................................................19

Assembly Statements..................................................................................................19

Symbol Names......................................................................................................22

Special Assembler Symbols..................................................................................24

viContents

Immediate Data .....................................................................................................25

Indirect Addresses.................................................................................................26

CODE and CONST †...........................................................................................26

EDATA †.............................................................................................................27

HDATA †.............................................................................................................27

Direct Data Addresses...........................................................................................27

Direct Bit Addresses..............................................................................................28

Program Addresses................................................................................................28

Relative Jumps ......................................................................................................28

In-Block Jumps and Calls (ACALL and AJMP)...................................................29 Long Jumps and Calls (LJMP and LCALL)..........................................................29 Extended Jumps and Calls (EJMP and ECALL)...................................................29 Generic Jump and Call (JMP and CALL) .............................................................29

Expressions and Operators..........................................................................................30

Character Strings...................................................................................................32

Location Counter...................................................................................................32

Arithmetic Operators.............................................................................................33

Binary Operators...................................................................................................34

Relational Operators..............................................................................................34

Class Operators .....................................................................................................35

Type Operators †..................................................................................................35

Miscellaneous Operators.......................................................................................36

Operator Precedence .............................................................................................37

Expression Classes................................................................................................38

Relocatable Expressions........................................................................................39

Simple Relocatable Expressions............................................................................39

Extended Relocatable Expressions........................................................................40

Chapter 4. Assembler Directives.....................................................................41

Segment Controls........................................................................................................42

Location Counter...................................................................................................42

Generic Segments..................................................................................................43

Stack Segment.......................................................................................................44

Absolute Segments................................................................................................44

Default Segment....................................................................................................45

BSEG, CSEG, DSEG, ISEG, XSEG.....................................................................50

Symbol Definition.......................................................................................................51

A51 Assembler / A251 Assembler vii

EQU, SET.............................................................................................................51

CODE, DATA, IDATA, XDATA.........................................................................52

LIT †....................................................................................................................54

Memory Initialization.................................................................................................56

DD †.....................................................................................................................57

Memory Reservation...................................................................................................58

DSB †...................................................................................................................59

DSW †..................................................................................................................60

DSD † ..................................................................................................................61

Procedure Declaration † ............................................................................................62

PROC / ENDP †...................................................................................................62

LABEL †..............................................................................................................64

Program Linkage.........................................................................................................65

EXTRN / EXTERN ..............................................................................................65

Address Control..........................................................................................................67

EVEN †................................................................................................................68

Other Directives..........................................................................................................71

Chapter 5. Standard Macros............................................................................73

Defining a Macro........................................................................................................74

Repeating Blocks..................................................................................................77

Nested Definitions.................................................................................................79

Nested Repeating Blocks......................................................................................80

Recursive Macros..................................................................................................80

Operators ....................................................................................................................81

NUL Operator.......................................................................................................81

& Operator............................................................................................................82

< and > Operators .................................................................................................83

% Operator............................................................................................................84

;; Operator.............................................................................................................85

! Operator..............................................................................................................85

viiiContents

Invoking a Macro........................................................................................................85

Chapter 6. Macro Processing Language.........................................................87

Creating and Calling MPL Macros .............................................................................87

Creating Parameterless Macros...................................................................................88

MPL Macros with Parameters.....................................................................................89

Local Symbols List......................................................................................................92

Macro Processor Language Functions ........................................................................93

Comment Function................................................................................................93

Escape Function ....................................................................................................94

Bracket Function...................................................................................................94

METACHAR Function .........................................................................................95

Numbers and Expressions .....................................................................................96

Character Strings...................................................................................................97

SET Function.........................................................................................................98

EVAL Function.....................................................................................................99

Logical Expressions and String Comparison.........................................................99

Conditional MPL Processing ....................................................................................100

IF Function..........................................................................................................101

WHILE Function.................................................................................................101

REPEAT Function...............................................................................................102

EXIT Function.....................................................................................................103

String Manipulation Functions..................................................................................103

LEN Function......................................................................................................104

SUBSTR Function...............................................................................................104

MATCH Function...............................................................................................105

Console I/O Functions...............................................................................................106

Advanced Macro Processing.....................................................................................107

Literal Delimiters ................................................................................................107

Blank Delimiters..................................................................................................108

Identifier Delimiters............................................................................................109

Literal and Normal Mode....................................................................................109

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