18-08-2012, 10:04 AM
The 8051 Instruction Set
[attachment=31948]
Introduction
The process of writing program for the microcontroller mainly consists of giving instructions (commands) in the specific order in which they should be executed in order to carry out a specific task. As electronics cannot “understand” what for example an instruction “if the push button is pressed- turn the light on” means, then a certain number of simpler and precisely defined orders that decoder can recognise must be used. All commands are known as INSTRUCTION SET. All microcontrollers compatibile with the 8051 have in total of 255 instructions, i.e. 255 different words available for program writing.
At first sight, it is imposing number of odd signs that must be known by heart. However, It is not so complicated as it looks like. Many instructions are considered to be “different”, even though they perform the same operation, so there are only 111 truly different commands. For example: ADD A,R0, ADD A,R1, ... ADD A,R7 are instructions that perform the same operation (additon of the accumulator and register). Since there are 8 such registers, each instruction is counted separately. Taking into account that all instructions perform only 53 operations (addition, subtraction, copy etc.) and most of them are rarely used in practice, there are actually 20-30 abbreviations to be learned, which is acceptable.
[attachment=31948]
Introduction
The process of writing program for the microcontroller mainly consists of giving instructions (commands) in the specific order in which they should be executed in order to carry out a specific task. As electronics cannot “understand” what for example an instruction “if the push button is pressed- turn the light on” means, then a certain number of simpler and precisely defined orders that decoder can recognise must be used. All commands are known as INSTRUCTION SET. All microcontrollers compatibile with the 8051 have in total of 255 instructions, i.e. 255 different words available for program writing.
At first sight, it is imposing number of odd signs that must be known by heart. However, It is not so complicated as it looks like. Many instructions are considered to be “different”, even though they perform the same operation, so there are only 111 truly different commands. For example: ADD A,R0, ADD A,R1, ... ADD A,R7 are instructions that perform the same operation (additon of the accumulator and register). Since there are 8 such registers, each instruction is counted separately. Taking into account that all instructions perform only 53 operations (addition, subtraction, copy etc.) and most of them are rarely used in practice, there are actually 20-30 abbreviations to be learned, which is acceptable.