AVR microcontroller serial communication program

　　The serial port of the microcontroller is often a useful communication interface. For example, if you want to modify some variables inside the microcontroller, you can directly use the serial port communication to send the parameters to the microcontroller, saving the trouble of recompiling and downloading.

　　　　The serial communication function of the AVR microcontroller is very powerful. Let me briefly talk about some of my experiences when learning it.

　　　　The experimental board is AVR-ATMEGA128A microcontroller, crystal oscillator 8MHz.

 

　　1. Initialization: Before setting the baud rate, close all uses of USART0, including enabling and interrupts.

　　2. Set UCSR0A: UCSR0A can write Bit0, Bit1, Bit6, and the other 5 bits are status bits. We generally use Bit1-U2X0. When this bit is 1, the baud rate division factor is reduced from 16 to 8, which can effectively double the transmission rate of the asynchronous communication mode. However, this bit only affects asynchronous operations and should be cleared when using synchronous operations.

　　3. Set UCSR0C: Bit6-UMSEL0:USART0 mode selection 0 for asynchronous mode, 1 for synchronous mode.

　　　　Bit5:4-UPM01:0: Parity check mode, 00 disabled, 01 reserved, 10 even check, 11 odd check.

　　　　Bit3-USBS0: Stop bit selection 0-stop bit is 1 bit, 1 stop bit is 2 bits

　　　　Bit2: 1-UCSZ01: 0: Character length When UCSZ02 is 0: 00 means 5 bits, 01 means 6 bits, 10 means 7 bits, and 11 means 8 bits. When UCSZ02 is 1, 11 means 9 bits (UCSZ02 is a register in UCSR0B).

　　4. Set UBRR: The setting of UBRR is related to these parameters: U2X0, CPU frequency, baud rate

　　5. Then set UCSR0B: Bit7-RXCIE0 is the reception end interrupt enable, Bit6-TXCIE0 is the transmission end interrupt enable, Bit4-RXEN0 is the reception enable, and Bit3-TXEN0 is the transmission enable. Generally, reception uses the interrupt mode, so the reception end interrupt enable is used.

 

 

Here is the source code:

 

/*
 * usart.c
 *
 * Created: 2011/7/2 15:48:36
 * Author: YIN
 */

#include
#include
#include
volatile unsigned char temp;
void init()
{
 UCSR0B=0x00;
 UBRR0H=0x00;
 UBRR0L=51;
 UCSR0A =0x00;
 UCSR0C=0x06;
 UCSR0B=0x98;
 sei();
 DDRF=0xff;
 PORTF=0xff;
 DDRD=0xf0;
 DDRA=0xff;
 
}
void delay()
{
 unsigned int i;
 i=100;
 while(i-- );
}

int main(void)
{
 init();
    while (1); //wait for interrupt
}

SIGNAL (SIG_UART0_RECV) //Send the data sent by the host computer back to the host computer for display
{
 temp=UDR0;
 PORTA=~temp;
 UDR0=temp;
}