Baud rate setting of Atmega32

[shahbaz.ele]

Dear all
I am using ATmega32 controller. serial port is interfaced here is code

baud = 12;

void rs_init(unsigned char baud)
{
UBRRL = baud;
UCSRC = (1<<URSEL)|(3<<UCSZ0);
UCSRB = (1<<RXEN) | (1<<TXEN);
}


void rs_send(unsigned char data)
{
while( !( UCSRA & (1<<UDRE)) );
UDR = data;
}

this code is working well.
baud rate 4800 at 1MHz

The problem is that now I want to set baud rate 9600 at 1Mhz how can I do this.
Is there any calculator of baud rate value for microcontroller speed?

 

[ud23]

http://www.wormfood.net/avrbaudcalc.php for ready made calculator

http://www.atmel.com/Images/AVR274.pdf use equestion given in this document

 

[3wais]

The maximum supported baud rate by an AVR is the CPU clock divided by 8
so when using 1 MHz clock you can use 125K buad rate
the baud rate can be calculated using this equation(found in datasheet)

Baud = Fosc / (16*(UBRR + 1))


instead of changing the baud rate u can just set the double speed bit (U2X) in the UCSRA register


you realise that according to the equation your baud rate with your freqyency can generate errors
consider using 7.3728 or 11.0592 crystals to eliminate the error

 

[shahbaz.ele]

Thanks you all
dear 3wais
after setting U2X, will it disturb my rest of code.
what do you mean by using 7.3728 or 11.0592 crystals, will it give errors by setting U2X bit.
I am not using any crystal at the moment

 

[alexxx]

after setting U2X, will it disturb my rest of code.

No this only has to do with the settings of USART. So don't worry, other peripherals will not be disturbed.

what do you mean by using 7.3728 or 11.0592 crystals, will it give errors by setting U2X bit.
I am not using any crystal at the moment

Those crystal values will give you no baudrate error according to the tables at pages 165-168. If you use the 8MHz internal RC, then you should look the table 70 in page 167 for 8Mhz clock. There is an error column for each clock frequency. So for 8MHz for example and double speed (U2X=1), 57.6K is not a good baudrate because you have an error of 2.1%. 38.4K on the other hand gives an error of 0.2%. Thus it is much more appropriate to choose 38.4K at 8MHz frequency.

http://www.atmel.com/Images/doc2503.pdf


Hope it helped,
Alexandros

 

[shahbaz.ele]

thanks dear alexxx
how can I set 8 Mhz frequency. and 38.4K baud rate

---------- Post added at 12:13 ---------- Previous post was at 12:12 ----------

without using crystal

 

[alexxx]

how can I set 8 Mhz frequency

From the fuse bits:
Int RC Osc, start-up time: 6CK + 65 ms, [CKSEL=0010 SUT=10].
Also: "Divide clock by 8 internally" (CKDIV8) disabled.

and 38.4K baud rate

It is in table 70 of the datasheet. UBRR=25, U2X bit of UCSRA register = 1. Keep in mind that UBRR is a 16-bit register. So for values < 255 (like 25 for instance), UBRRH stays 0 and 25 goes to UBRRL.