Re: [avr-chat] 16Mhz or bust

[Jesper Hansen]

Your UBBR value seems a bit off. The UBBRH and UBBRL registers are only
8-bit and you're loading a 16-bit value to it.
Also, for 2400 bps at 16 MHz, I get the value 415 (or 416 depending on
rounding), and not 432.
Here's the "classic" code that many people use :

#define F_CPU    16000000
.
.
#define UART_BAUD_RATE   115200
#define UART_BAUD_SELECT  (uint16_t) ((uint32_t)F_CPU /
((uint32_t)UART_BAUD_RATE * 16L) - 1)
.
.
 // set baud rate
 UBBRH  =  UART_BAUD_SELECT   >> 8;
 UBBRL = UART_BAUD_SELECT  & 0xff;


/Jesper

----- Original Message ----- 
From: "Mikey Sklar" <address@hidden>
To: <address@hidden>
Sent: Tuesday, August 16, 2005 2:37 AM
Subject: [avr-chat] 16Mhz or bust


> I have been working with a ATmega32 through a stk500 under Mac OS/X.
> I've had no trouble getting a little test serial program working through
> the USART using the 1MHz default internal oscillator. However, I have
> had no luck working at running the MCU at higher speeds than 1MHz.
>
> I'm sure someone must have been successful using a AT part at greater
> than 1MHz. What am I missing here?
>
> Knobs I've been frobing with:
>  (note: these settings are known **BAD!**)
>
> - Configuring the ATmega32 for 16MHz
>  * stk500 - external 16MHz crystal installed
>  * stk500 - XTAL1 unjumpered
>  * stk500 - OSCSEL - pins 2,3 jumperred
>  * Fuse high byte - CKOPT - 10011001 (uisp --wr_fuse_h=0x99)
>  * Fuse low byte - CKSEL - 11101111 (uisp --wr_fuse_l=0xEF)
>  * OSCCAL --wr_osc=16000000 (sets to 3686400, perhaps unsigned int  issue)
>  * src code - 16MHz @ 2400bps UBRRL=432 or UBRRL=1B0
>
> I've been using 'uisp' to set the fuse bits. I see at least one issue
> with uisp not taking a clock value over 3.6864Mhz. I'm aware of the
> usual mistakes:
>
> - Internal oscillator maxes at 8MHz
> - Fuse bits are inversed logic (0 is enabled)
>
>
>
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