在AVR Atmega88-PA上设置UART时遇到问题

Question

I want to set up the UART on a ATmega88-PA. First I was trying to set an interrupt on UDRE register but this was not working, so for the transmission I use normal polling. Because the code was not working I started again from 0 with a basic program.

#define F_CPU 1000000UL
#define USART_BAUDRATE 9600
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 8UL))) - 1)

char ReceivedByte = '#';

int main (void)
{
    UCSR0A = (1 << U2X0);

    /* Turn on the transmission and reception circuitry. */
    UCSR0B = (1 << RXEN0) | (1 << TXEN0);
    /* Use 8-bit character sizes. */
    //UCSR0C = (1 << UCSZ00) | (1 << UCSZ01);

    /* BAUD prescale */
    UBRR0 = 12;

    /* Load upper 8-bits of the baud rate value into the high byte of the UBRR register. */
    //UBRR0H = (BAUD_PRESCALE >> 8);
    /* Load lower 8-bits of the baud rate value into the low byte of the UBRR register. */
    //UBRR0L = BAUD_PRESCALE;

    UCSR0B |= (1 << RXCIE0);

    sei();
    DDRB |= 0x04;
    PORTB &= ~0x04;

    for (;;)
    {
        /* Do nothing until data have been received and is ready to be read from UDR. */
        //while ((UCSR0A & (1 << RXC0)) == 0) {};
        /* Fetch the received byte value into the variable "ByteReceived". */
        //ReceivedByte = UDR0;

        if(ReceivedByte == '1')
            PORTB |=0x04;
        else
            PORTB &=~0x04;

        /* Do nothing until UDR is ready for more data to be written to it. */
        while ((UCSR0A & (1 << UDRE0)) == 0) {};
        /* Echo back the received byte back to the computer. */
        UDR0 = ReceivedByte;
    }
}

ISR(USART_RX_vect)
{
    ReceivedByte = UDR0;
}

And the code is working but when I open an arduino serial monitor and connect my module to that, I receive my poor # but alog with some garbage. Not all the time but mostly, the garbage is 1 or 2 byte. Can someone help me?

EDIT: It seams that when I send from my bleutooth data to a Samsung galaxy S3 the data is perfect...I do not have any clue why on serial monitor, and also when sending data using the same bluetooth to laptop I got a lot of garbage along with the data. If this helps you answearing my qestion, will be great.

EDIT: sorry forget the last edit, it is send only a char ok, I change the char and also garbage is there. When I send a string is unreadable.

EDIT : As I commneted on the post below of embedded_guy , I solve the problem inserting a _delay_ms(1) after sending each byte. and it is working right now. I believe the statement

 while ((UCSR0A & (1 << UDRE0)) == 0) {};

is not doing its job. Hope this will help others.

Answer 1

I don't know if this will work for you, but I really only see a couple of things that could be an issue.

First, all of the examples of setting the BAUD prescale that I could find used two instructions with the high and low registers of UBRR0 . If you have already stepped through your code and examined that register to ensure that it is correctly configured, then that is not the issue. Otherwise, I would recommend setting it like this for the value you have it set to in your code:

UBRR0H = 12;
UBRR0L = 0;

The other thing I see is that you are never setting UCSR0C . You have it commented out and I would expect it to operate correctly with its default (reset condition) settings, but it is always good to be explicit just in case.

Finally, you may want to take a look at this page on Simple Serial Communications .

EDIT
Based on your most recent edit, I would take the bluetooth out of the picture. I would recommend connecting a logic analyzer to the UART transmit pin of your microcontroller and see if the data coming out of the atmega is what you expected. If that data is good, I would begin looking at why the bluetooth is not working as I anticipated.

Answer 2

尝试使用至少2MHz的F_CPU

Answer 3

使您的ReceivedByte易失，像这样尝试：

volatile unsigned char ReceivedByte;