ADC MC9S08QG8, 10bit or 12bit ??

Brasil — Tue, 13 Mar 2007 04:59:02 GMT

I'm using MC9S08QG8 ADC module with the code:

SOPT1 = 0b01010010; //Pino Reset como I/O. COP desativado, DEBUG habiliado.
SOPT2 = 0b00000000; //I2C nos pinos PTA2 e PTA3.
ICSC2 = 0b00101111;
ICSC1 = 0b00111000;

//Configuração do Conversor AD:
ADCSC2 = 0;
ADCCFG = 0b01010100; //Clock ADC, Modo de consumo.
APCTL1 = 0b00000010; //Pinos usados pelo ADC.

//Função que faz a leitura do canal AD.
//Recebe: Canal do AD para efetuar a leitura.
//Retorna: Valor lido (10bit).
unsigned int ler_ad(unsigned char canal)
{
unsigned char conta = 8;
unsigned int temp =0;

while(conta)
{
ADCSC1 = (0b00000000 | canal); //Pega o canal (5 LSBs).

while(!ADCSC1_COCO); //Aguarda conversão...
temp += ADCR;
conta--;
delay_ms(2);
}

ADCSC1 = 0b00011111; //Desliga o ADC.

return temp >>3 ; //Divide por 8 (que foi o número de conversões).

}

The function 'int ler_ad(unsigned char canal)' it is returning a 12bit value, varying of 0 to the 4095 (varying the tension of pin PTA1 from 0V to VDD).
what it is happening ??! Datasheet says that the AD converter is of 10 bit but it seems that in the practical it works as if was an 12bit ADC!!

I'm using an 4MHz external crystal whith a 8MHz BUSCLK.

Re: ADC MC9S08QG8, 10bit or 12bit ??

peg — Tue, 13 Mar 2007 05:44:03 GMT

Hi Brasil,

Ths analogue converter is only 10-bit, 0 to 1023.

You have set the conversion mode incorrectly, you have selected a reserved setting in MODE in ADCCFG. This could be causing strange behaviour.

topic ADC MC9S08QG8, 10bit or 12bit ?? in 8-bit Microcontrollers

ADC MC9S08QG8, 10bit or 12bit ??

Re: ADC MC9S08QG8, 10bit or 12bit ??