Introduction to MCU C language

Tearful blue shirt 2021-02-23 17:30:11
introduction mcu language

Learn a programming language , The most important thing is to create a practice environment , Only by learning and practicing can we learn well .Keil Software is currently the most popular development 80C51 Series of MCU software ,Keil Provided include C compiler 、 Macro assembly 、 The connector 、 Library management and a powerful simulation debugger, etc , Through an integrated development environment (?Vision) Put these parts together .

Please install before learning KEILC51 Software , After learning to use assembly language , Study C Language programming is a relatively easy thing , We will introduce... Through a series of examples C Language programming methods . chart 1-1 The circuit diagram shown uses 89c51 Single chip microcomputer as the main chip , This property belongs to 80C51 series , It has 8K Of FLASH ROM, It can be repeated , It's perfect for experiments .89c51 Of P1 Pin on 8 A light-emitting diode ,P3.2~P3.4 Pin on 4 A button switch , Our task is to get the receiver to P1 The LED on the pin lights up as required .

 Single chip microcomputer C Language introduction tutorial

1 ordinary C Program is introduced

example 1-1: Let's connect P1.0 On the pin LED Luminescence .


Single light flashing program


#include "reg51.h"// This sentence will 51 Common ports for , The definition files of internal registers and so on are included in this program

sbit P1_0=P1^0;

void main()

{ P1_1=0;


The purpose of this program is to connect P1.0 On the pin LED Lighten up . Let's analyze this C What information does a language program contain .

1)" File contains " Handle .

The first line of the program is a " File contains " Handle .

So-called " File contains " It means that one file includes all the contents of another file , So the program here is just 4 That's ok , but C The compiler processes dozens or hundreds of lines . Here the program contains REG51.h The purpose of the document is to use P1 This symbol , Notice C compiler , What's written in the program P1 Refer to 80C51 Single chip microcomputer P1 Ports, not other variables . How can this be done ?

open reg51.h You can see something like this :


Header file for generic 80C51 and 80C31 microcontroller.

Copyright (c) 1988-2001 Keil Elektronik GmbH and Keil Software, Inc.

All rights reserved.


/* BYTE Register */

sfr P0 = 0x80;

sfr P1 = 0x90;

sfr P2 = 0xA0;

sfr P3 = 0xB0;

sfr PSW = 0xD0;

sfr ACC = 0xE0;

sfr B = 0xF0;

sfr SP = 0x81;

sfr DPL = 0x82;

sfr DPH = 0x83;

sfr PCON = 0x87;

sfr TCON = 0x88;

sfr TMOD = 0x89;

sfr TL0 = 0x8A;

sfr TL1 = 0x8B;

sfr TH0 = 0x8C;

sfr TH1 = 0x8D;

sfr IE = 0xA8;

sfr IP = 0xB8;

sfr SCON = 0x98;

sfr SBUF = 0x99;

/* BIT Register */

/* PSW */

sbit CY = 0xD7;

sbit AC = 0xD6;

sbit F0 = 0xD5;

sbit RS1 = 0xD4;

sbit RS0 = 0xD3;

sbit OV = 0xD2;

sbit P = 0xD0;

/* TCON */

sbit TF1 = 0x8F;

sbit TR1 = 0x8E;

sbit TF0 = 0x8D;

sbit TR0 = 0x8C;

sbit IE1 = 0x8B;

sbit IT1 = 0x8A;

sbit IE0 = 0x89;

sbit IT0 = 0x88;

/* IE */

sbit EA = 0xAF;

sbit ES = 0xAC;

sbit ET1 = 0xAB;

sbit EX1 = 0xAA;

sbit ET0 = 0xA9;

sbit EX0 = 0xA8;

/* IP */

sbit PS = 0xBC;

sbit PT1 = 0xBB;

sbit PX1 = 0xBA;

sbit PT0 = 0xB9;

sbit PX0 = 0xB8;

/* P3 */

sbit RD = 0xB7;

sbit WR = 0xB6;

sbit T1 = 0xB5;

sbit T0 = 0xB4;

sbit INT1 = 0xB3;

sbit INT0 = 0xB2;

sbit TXD = 0xB1;

sbit RXD = 0xB0;

/* SCON */

sbit SM0 = 0x9F;

sbit SM1 = 0x9E;

sbit SM2 = 0x9D;

sbit REN = 0x9C;

sbit TB8 = 0x9B;

sbit RB8 = 0x9A;

sbit TI = 0x99;

sbit RI = 0x98;

be familiar with 80C51 Readers of the internal structure can see that , Here are some definitions of symbols , That is to say, the corresponding relationship between symbol name and address is stipulated . Notice that there are

sfr P1 = 0x90;

Such a line ( It is shown in bold above ), By defining P1 And address 0x90 Corresponding ,P1 My address is 0x90(0x90 yes C How to write hexadecimal numbers in a language , It is equivalent to writing in assembly language 90H).

You can also see a word that appears frequently here :sfr

sfr And standards C Keywords of language , It is Keil In order to have direct access to 80C51 Medium SFR And a new keyword , Its usage is :

sfrt Variable name = Address values .

 Single chip microcomputer C Language introduction tutorial

2) Symbol P1_0 To express P1.0 Pin .

stay C In language , If you write directly P1.0,C The compiler doesn't recognize , and P1.0 It's not a legal C Language variable name , So we have to give it a different name , It's called P1_0, But P1_0 Is it P1.0 Well ? You think so ,C The compiler doesn't think so , So they have to be connected , It's used here Keil C Key words of sbit To define ,sbit There are three ways to use :

The first method :sbit Bit variable name = Address values

The second method :sbit Bit variable name =SFR name ^ Variable bit address value

The third method :sbit Bit variable name =SFR Address values ^ Variable bit address value

As defined PSW Medium OV There are three ways :

sbit OV=0xd2 (1) explain :0xd2 yes OV Bit address value of

sbit OV=PSW^2 (2) explain : among PSW Must use first sfr Well defined

sbit OV=0xD0^2 (3) explain :0xD0 Namely PSW Address value of

So here we use sfr P1_0=P1^0; It's defined by symbols P1_0 To express P1.0 Pin , You can get up if you want P10 A kind of name , As long as the following program is also changed .

3)main be called " The main function ".

every last C Language programs have and only have one main function , Tangent must have a main function , It is placed in a position that does not require , You can put it at the end of the program ( recommend ), There must be a pair of braces after the function "{}", Write other programs in braces .

From the above analysis, we understand part of C Characteristics of language , Let's take a more complicated example .

example 1-2 Let's connect P1.0 On the pin LED Twinkle


Single light flashing program


#include "reg51.h"

#define uchar unsigned char

#define uint unsigned int

sbit P10=P1^0;

/* Delay program

from Delay Parameters determine the delay time


void mDelay(unsigned int Delay)

{ unsigned int i;


{ for(i=0;i<124;i++)




void main()

{ for(;;)

{ P10=!P10; // Take the opposite P1.0 Pin




Program analysis : The main program main Let's not look at the first line in , The second line is "P1_0=!P1_0;", stay P1_0 There's a sign in front of it "!", Symbol "!" yes C A language operator , It's like in mathematics "+"、"-" equally , It's a kind of operation , Meaning is " Take the opposite ", That is to say, reverse the value of the variable after the symbol .

 Single chip microcomputer C Language introduction tutorial

Be careful : Negation is only for the value of a variable , It doesn't automatically change the variable itself . It can be said that C The compiler is dealing with "!P1_0" when , take P1_0 The value of gives a temporary variable , And then reverse the temporary variable , Not directly to P1_0 Take the opposite , Therefore, the assignment symbol should be used after negation ("=") Assign the negated value to P1_0, such , If the original P1.0 Is a low level (LED bright ), So after the reversal ,P1.0 It's high level (LED destroy ), conversely , If P1.0 Is a high level , After reverse ,P1.0 It's low level , This command is executed over and over again , Connect to P1.0 When you put on the light, it keeps going " bright "、" destroy ".

The key to this instruction being repeated is main The first line of the program in :for(;;), This is not detailed here , For the time being, readers just need to know , This line of program is followed by a pair of braces "{}" Constitutes an infinite loop statement , The statement in the braces is executed repeatedly .

The third line is :"mDelay(1000);", The purpose of this line of programs is to delay 1s Time , Because the speed of single chip microcomputer executing instructions is very fast , If there is no delay , The light goes out as soon as it comes on , It's on right after it's off , Too fast , The human eye can't tell .

here mDelay(1000) Not by Keil C Library functions provided , That is, you can't write such a program to achieve delay under any circumstances . If you write this line when you write other programs , You'll find that compilation doesn't work . So why is it right here ? observe , You can see that there are void mDelay(…) This line of business , so ,mDelay The word is our own name , And wrote some program lines for this , If you don't have such a program line in your program , Then you can't use mDelay(1000) 了 . Some people have quick brains , It may come to mind right away , Can I copy this program to my other programs as well , And then you can use it mDelay(1000) What about it ? The answer is , Of course, that's OK . One more point needs to be made ,mDelay The name is given by the programmer himself , You can change it yourself , But once you change the name ,main() The name of the function needs to be changed accordingly .

mDelay There's a parenthesis behind it , There's data in parentheses (1000), This 1000 It's called " Parameters ", It can be used to adjust the delay time in a certain range , Here we use 1000 To ask for a delay time of 1000 millisecond , Do that , It has to be written by ourselves mDelay It was decided by that procedure .

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