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Ax51 Introduction

This manual describes the macro assemblers and utilities for the classic 8051 and extended 8051 microcontroller families and explains the process of developing software in assembly language for these microcontroller families.

A brief overview of the classic 8051, and the extended 8051, and the 251 architectures may be found in the Instruction Set User's Guide, Architecture Overview. In this overview, the differences between the classic 8051, the extended 8051 variants and the 251 processors are described. For the most complete information about the microcontroller architecture refer to the hardware reference manual of the microcontroller derivative that your are using.

For optimum support of the different 8051 and 251 variants, Keil provides the following development tools:

Development Tools Support Microcontrollers Description
A51 Macro Assembler
BL51 Linker/Locater
LIB51 Library Manager
Development Tools for classic 8051.
Includes support for 32 x 64KB code banks.
AX51 Macro Assembler
LX51 Extended Linker/Locater
LIBX51 Library Manager
Development Tools for classic and extended 8051 versions (NXP 80C51MX, Dallas 390, etc.) Supports up to 16MB code and xdata memory.
A251 Macro Assembler
L251 Linker/Locater
LIB251 Library Manager
Development Tools for the 251.

The AX51 assembler is a superset of the A51 assembler. This user's guide therefore covers all development tools variants. Whenever a feature or an option is available in one specific tool chain only, it is clearly marked.

For general reference to all tool variants and microcontroller architectures the terms listed in the following table are used:

Term Refers to ...
Ax51 Macro Assembler A51, AX51 and A251 Macro Assembler .
Cx51 Compiler C51, CX51 and C251 ANSI C Compiler.
Lx51 Linker/Locator BL51, LX51 and L251 Linker/Locator.
LIBx51 Library Manager LIB51, LIBX51 and LIB251 Library Manager.
OHx51 Object-Hex Converter OH51, OHX51 and OH251 Object-Hex Converter.
x51 Architecture or x51 Device All classic 8051, extended 8051 and 251 device variants.
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