Single chip microcomputer (STC series 8051 core single chip microcomputer)

1. Number system

• To better describe and remember the address of the microcomputer , The code is generally hexadecimal .
• Original code , Inverse and complement
  The inverse code and complement of positive numbers are the same as the original code , The inverse of a negative number is : Keep the original code symbol bit unchanged , The digits of the value are reversed ; The complement of a negative number is : Take the reverse and add one .
  All signed numbers in a computer are represented by complements ( Positive numbers have the same form , It can be thought that the original code is used to express ), The result of the operation is also a complement .

2. Microcomputer principle

• Von Neumann structure : A computer consists of an arithmetic unit , controller . Memory , Input devices and output devices are made up of .
• Microcomputer structure : A single chip microcomputer consists of a microprocessor (CPU), Memory , I / O interface (I/O Interface ) And the bus ( Address bus , Data bus and control bus ) form ; In addition, the input and output equipment is the system machine ( Such as PC machine ).
• programing language
  machine language .
  assembly language : Use English mnemonics to describe instructions ; Need to compile .
  High-level language : Natural language description ; Need to compile .
• Microcomputer working process
  Fingering , Instruction decoding , Execution instruction .

3. Single chip microcomputer instruction system

• Assembly language instruction format
  label opcode Operands .
• Addressing mode
  How to find operands when executing instructions .
• Transmitted by data ( Instructions ), Arithmetic operation , Logical operations , Shift operation , Bit operation and control transfer constitute .

4. C51 Application framework

• Pretreatment part
  ( Such as include “stc15.h”# Contains the SCM header file ,include “GPIO.h”# Contains initialization I/O Port header file )
• Global variable definitions and function declarations
• The main function
• Subfunctions and interrupt service functions

5. Important functions of single chip microcomputer / form

• Memory :RAM,ROM
• timing / Counter
• Interrupt the system .
  Task scheduling / Resource sharing / human-computer interaction .
  send CPU It has the ability to deal with external emergencies in real time .
  Interrupt the process : Interrupt request , Interrupt response , Interruption of service , Interrupt return .
• Serial port .
  asynchronous / Sync ; Simplex / Half duplex / full duplex .
• A/D Conversion module .
  principle : Step by step .
• PWM( Pulse width modulation )
  Use the duty ratio of square wave to encode the level of analog signal ,PWM The signal is digital , But as long as the bandwidth is enough , Any analog value can be used PWM Encoding , Can be realized D/A transformation .
  High resolution counter implementation PWM.
• human-computer interaction
  LED Digital display : Static display , Dynamic scanning display ( Each has its own string / Parallel display mode ).
  LCD Liquid crystal display (LCD) : Digital display pen segment , dot character , Lattice graphics .
• keyboard
  Independent buttons .
  Matrix keyboard : Scanning ( Query scan , Time scan , Interrupt scan ) And line reversal method .
• watchdog
  Reliability design , If cpu Fail to visit the watchdog as required within the specified time , The watchdog will force a reset cpu.