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:

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: