STC89C52 serial port application example

1) Hardware Design
Generally, the serial port communication of a microcontroller needs to be converted by MAX232 for level conversion before data communication. Of course, the STC89C52RC microcontroller is no exception. The connection method in the figure is the simplest connection of the commonly used zero-modem method, that is, the 3-wire connection method: only the RXD, TXD and GND lines are used, as shown below.

STC89C52 serial port application example

Since the logic "0" level of RS232 is specified as +5~+15V, and the logic "1" level is specified as -15~-5V, it cannot be directly connected
to the TTL/CMOS circuit and must be converted.
Level conversion can be achieved using discrete devices such as transistors, or a dedicated level conversion chip, MAX232 is a typical
one. MAX232 can not only achieve level conversion, but also realize mutual conversion of logic, that is, positive logic to negative logic.
#include "stc.h" //Load "stc.h" header file
void Delay(void) //Define Delay function, delay 500ms
{
unsigned char i,j; //Declare variables i,j
for(i=0;i<255;i++) //Perform loop operation to achieve the delay effect
for(j=0;j<255;j++);
for(i=0;i<255;i++) //Perform loop operation to achieve the delay effect
for(j=0;j<255;j++); for(i=0;i<255;i++) //Perform loop operation to achieve the delay effect for(j=0;j<255;j++);
for(i=0;i<255;i++) //Perform loop operation to achieve the delay effect
for(j=0;j<140;j++);
}


void UARTInit(void) //Define serial port initialization function
{
SCON =0x40; //8-bit data bit
T2CON=0x34; //T/C2 is used as the baud rate generator
RCAP2L=0xD9; //The baud rate is 9600 The lower 8 bits of
RCAP2H=0xFF; //The higher 8 bits of the baud rate is 9600
}


void UARTSendByte(unsigned char byte)//Serial port sends a single byte function
{
SBUF=byte; //The buffer loads the byte to be sentwhile
(TI==0); //Wait for the sending to be completed, the TI flag will be set to 1
TI=0; //Clear the sending completion flag
}
void main(void) //Enter the Main function
{
unsigned char i=0; //Declare variable i
UARTInit(); //Serial port initializationwhile
(1) //Enter an infinite loop
{
UARTSendByte(i); //Serial port sends a single byte of dataDelay
(); //Delay 500ms
i++; //i adds 1
if(i>255)i=0; //If i>255,i=0
}
}