A251 Introduction

This manual describes the macro assembler for the 251 microcontroller family and explains the process of developing software in assembly language for these microcontroller families.

A brief overview of the classic 8051, 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 and A251 assemblers are supersets of the A51 assembler. This user's guide only covers the 251 development tool variant. However, for general reference to all tool variants and microcontroller architectures the terms listed in the following table are used: