51 single-chip computer serial communication

First, learn some basic concepts.

RS232 Level: Logic 1 (MARK) =-3v~-15v, Logic 0 (SPACE) =+3~+15v

TTL level: + + is equivalent to logic "1", 0V equivalent to logic "0"

TXD: Send data transmit the P31 of single chip microcomputer

RXD: Receiving data, P30 of MCU

Baud rate: The rate at which a single-chip or computer communicates at the serial port, defined as the number of bits transmitted in binary code per second, unit BTS

UART: Universal Asynchronous Transceiver. 51 MCU serial Port is a programmable full-duplex communication interface, with the full function of the UART, the data can be sent and received at the same time, it can also be used as a synchronous shift register.

SBUF: Serial Data buffer Register

Often use communication Mode 1 (10-bit data asynchronous communication, baud rate variable, timer 1), so must master ~ ~ ~

Timer 1 Common mode 2, when overflow, the single-chip opportunity to automatically install the initial value, mode 1 need to manually install the initial value

Attached: Common baud rate initial value table

/*		send character  @L2  2016/08/08 */
#include <reg51.h>
unsigned char word[19] = "nice to meet you!";
void Init ();
void delay10ms (unsigned int c);

void Main ()
{
	unsigned char i;
	Init ();
	while (1)
	{for
		(i=0; i<19; i++)
		{
			sbuf = word[i];   The data to be sent is put into the Send register while
			(! TI);		  Wait for send data to complete: When the serial send 8th bit of data ends, the internal hardware is 1.
			ti=0;			  Clear send completion flag bit: Software clear 0
		}
		delay10ms;		  Delay and then send
	}
}

void init ()				  //Set serial port
{
	scon=0x50;			Set to Working mode 1   SMO SM1 SM2 ren=0 1 0 1  
	tmod=0x20;			Set Timer 1 working mode 2
	pcon=0x80;			Baud rate doubled	smod=1
	th1=0xe6;		    The counter initial value is set, where the baud rate is 2400
	tl1=0xe6;	Es=1;						Open receive interrupt
//	ea=1;						Open total interrupt
	tr1=1;					    Open counter
}


void delay10ms (unsigned int c)   //Error 0us
{
    unsigned char a, b;
    for (; c>0;c--)
	{for
		(b=38;b>0;b--)
		{for
			(a=130;a>0;a--);       
}}}

			the/** will receive a send back to the computer. @L2  2016/08/08 		**/

#include <reg51.h>

void init ()			  //Set serial port
{
	scon=0x50;			Set to Working mode 1
	tmod=0x20;			Set the counter mode of Operation 2
	pcon=0x80;			Baud rate doubled
	th1=0xf3;		    The counter initial value is set, note that the baud rate is 4800
	tl1=0xf3;
	Es=1;						Open receive interrupt
	ea=1;						Open total interrupt
	tr1=1;					    Open counter
}

void Usart () Interrupt 4	 //serial port interrupt, serial ports complete a frame character send/Receive after
{
	unsigned char receivedata;

	receivedata=sbuf;//go out to receive the data
	RI = 0;           Clears the receive interrupt flag bit
	sbuf=receivedata;//puts the received data into the Send register while
	(! TI);		  Waiting to send data to complete
	ti=0;			  Clear send completion flag bit
}

void Main ()
{
	init ();
	while (1)
	{
	}
}