1, Pointer basis

In the single chip microcomputer, the total memory size is 512M, including 216M in chip and 216M out of chip. Pointer, in bytes.
char: 1 byte
int: 2 bytes
long: 4 bytes

Define a pointer: * P
Go to the address of a variable: & P
The pointer is also a variable, but the variable stores an address, and the layout directly assigns a value to the pointer


sizeof is a constant that returns the byte size of a variable.

Example 1:

#include<reg52.h>

sbit ADDR0 = P1^0;
sbit ADDR1 = P1^1;
sbit ADDR2 = P1^2;
sbit ADDR3 = P1^3;
sbit ENLED = P1^4;

void ShiftLeft(unsigned char *p);//Parameter is an address

void main()
{
	unsigned int i;
	unsigned char buf = 0x01;

	ENLED = 0;
	ADDR3 = 1;
    ADDR2 = 1;
    ADDR1 = 1;
    ADDR0 = 0;

	while(1)
	{
		P0 = ~buf;
		for(i = 0;i<20000;i++);
		ShiftLeft(&buf);//Get the address of buf, move left one bit at a time, change the value of buf
		if(buf == 0)
		{
			buf = 0x01;
		}
	}
}

void ShiftLeft(unsigned char *p)
{
	*p = *p<<1;
}

Example two:

#include<reg52.h>

bit cmdArrived = 0;//Check whether the upper computer sends the command. If it sends the command, set one
unsigned char cmdIndex = 0;
unsigned char *ptrTxd;
unsigned char cntTxd = 0;

unsigned char array1[1] = {1};
unsigned char array2[2] = {1,2};
unsigned char array3[4] = {1,2,3,4};
unsigned char array4[8] = {1,2,3,4,5,6,7,8};

void ConfigUART(unsigned int baud);

void main()
{
	EA = 1;//Enable total interrupt
	ConfigUART(9600);

	while(1)
	{
		if(cmdArrived)//Message sent by upper computer detected
		{
			cmdArrived = 0;
			switch(cmdIndex)
			{
				case 1:
					ptrTxd = array1;
					cntTxd = sizeof(array1);
					TI = 1;	//Send out
					break;
				case 2:
					ptrTxd = array2;
					cntTxd = sizeof(array2);
					TI = 1;
					break;
				case 3:
					ptrTxd = array3;
					cntTxd = sizeof(array3);
					TI = 1;
					break;
				case 4:
					ptrTxd = array4;
					cntTxd = sizeof(array4);
					TI = 1;
					break;
				default:
					break;	
			}
		}
	}
}

void ConfigUART(unsigned int baud)
{
    SCON  = 0x50;  //Configure serial port as mode 1
    TMOD &= 0x0F;  //Reset the control bit of T1
    TMOD |= 0x20;  //Configure T1 as mode 2
    TH1 = 256 - (11059200/12/32)/baud;  //Calculate T1 overload value
    TL1 = TH1;     //Initial value equal to overload value
    ET1 = 0;       //Disable T1 interrupt
    ES  = 1;       //Enable serial port interrupt
    TR1 = 1;       //Start T1
}

void InterruptUART() interrupt 4
{
	if(RI)//If reception is complete
	{
		RI = 0;
		cmdIndex = SBUF;//Index number
		cmdArrived = 1;
	}

	if(TI)//Send out
	{
		TI = 0;
		if(cntTxd > 0)
		{
			SBUF = *ptrTxd;
			cntTxd--;
			ptrTxd++;//Send next element
		}

	}
}

2, Character array and character pointer

The string constant 'a' has a null value \ 0 more than the character constant 'a', which is one more byte.

3, 1602 liquid crystal

#include<reg52.h>

#define LCD1602_DB P0
sbit LCD1602_RS = P1^0;//Data command control bit
sbit LCD1602_RW = P1^1;//Read write control bit
sbit LCD1602_E = P1^5;//Enabling position
void InitLcd1602();
void LcdShowStr(unsigned char x,unsigned char y,unsigned char *str);

void main()
{
	unsigned char str[] = "Kingst Studio";
	InitLcd1602();
	LcdShowStr(2, 0, str);
	LcdShowStr(0, 1, "Welcome to KST51");
	while(1);
}

void LcdWaitReady()	//Read state
{
	unsigned char sta;

	LCD1602_DB = 0xFF;//High level before reading
	LCD1602_RS = 0;//Data pattern
	LCD1602_RW = 1;//Reading mode
	do {
		LCD1602_E = 1;
		sta = LCD1602_DB;//Pass LCD status to sta
		LCD1602_E = 0;//In order not to affect other peripherals, turn off the enable bit
		}while(sta & 0x80);//When the highest bit is 1, the LCD is busy and cannot be operated

}

void LcdWriteCmd(unsigned char cmd)	//Write instruction
{
	LcdWaitReady();//Determine whether reading and writing operation can be performed
	LCD1602_RS = 0;
	LCD1602_RW = 0;
	LCD1602_DB = cmd;//Data writing
	LCD1602_E = 1;//Start writing
	LCD1602_E = 0;//Write off
}

void LcdWriteDat(unsigned char dat)//Writing data
{
	LcdWaitReady();
   	LCD1602_RS = 1;
	LCD1602_RW = 0;
	LCD1602_DB = dat;//Data writing
	LCD1602_E = 1;
	LCD1602_E = 0;
}

void LcdSetCursor(unsigned char x,unsigned char y)//Display coordinate settings
{
	unsigned char addr;
	if(y == 0)//In the first line
	{
		addr = 0x00 + x;
	}	
	else//In the second row
	{
		addr = 0x40 + x;
	}
	LcdWriteCmd(addr | 0x80);
}

void LcdShowStr(unsigned char x,unsigned char y,unsigned char *str)
{
	LcdSetCursor(x,y);
	while(*str != '\0')
	{
		LcdWriteDat(*str++);
	}
}

void InitLcd1602() //Lcd initialization
{
	LcdWriteCmd(0x38);
	LcdWriteCmd(0x0C);
	LcdWriteCmd(0x06);
	LcdWriteCmd(0x01);
}

Conclusion:

In this project, the function is written from top to bottom, which is divided into different modules, and the modules call each other.