Re: [avr-gcc-list] UART transmitting problem

[Bob Paddock]

> #define F_CPU            4000000      /* 4Mhz */
> #define UART_BAUD_RATE      9600      /* 9600 baud */
> #define UART_BAUD_SELECT (F_CPU/(UART_BAUD_RATE*16l)-1)

Always check to see what is really being generated by that type of formula.

I've run into some combinations of crystals and baud rates give a answer that
is off by one due to the integer truncation of the math.

>       while ( ( c = *(buf++) ) != '\0' ) {
>               loop_until_bit_is_set( USR, UDRE );
>               outp( c, UDR );

Are you sure that UDRE will be set BEFORE you send the first char?
I've been bitten by a problem like that recently.   The UART Shift Register 
empty bit comes up zero from reset, not set like you would want.


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