ARM Getting Started Notes (5)

 Analog Input

- A/D Conversion Experiment

I. Purpose

Through A/D conversion, the voltage value of the external analog input channel can be correctly read.

II. Experimental procedures and parameter settings

1> The connector option settings and startup code are the same as the previous experiment
2> C language code

#i nclude "AT91SAM7S64.h"
#i nclude "Board.h"
volatile unsigned int EXT_AD_Val[4]; //Define A/D conversion result value
int main(void)
{unsigned char i;
*AT91C_ADC_CR = AT91C_CKGR_MOSCEN; //Software reset of ADC, that is, clear all registers of ADC
*AT91C_PMC_SCER = AT91C_CKGR_MOSCEN; //Enable the processor clock of the system clock register
*AT91C_PMC_PCER = 1 91C_ID_ADC; //Enable ADC clock
*AT91C_PIOA_PDR = EXT_AD0 | EXT_AD1; //Disable the I/O port function of the pin and use it as analog input function
*AT91C_ADC_MR = 0x0f1f3f00; //Software start, 10-bit resolution, 128 division
*AT91C_ADC_CHER = 0x33; //Enable channels 0, 1, 4, 5
*AT91C_ADC_CHDR = 0xcc; //Disable channels 2, 3, 6, 7
*AT91C_ADC_IDR = 0xfffff; //Disable all ADC interrupts
while (1)
{ *AT91C_ADC_CR = 0x2; //Start conversion
while (1)
{ if ((*AT91C_ADC_SR) & 0x33) //Wait for conversion to end
  { EXT_AD_Val[0] = (*AT91C_ADC_CDR0) & 0x3ff; //Read 10-bit result value
   EXT_AD_Val[1] = (*AT91C_ADC_CDR1) & 0x3ff;
   EXT_AD_Val[2] = (*AT91C_ADC_CDR4) & 0x3ff;
   EXT_AD_Val[3] = (*AT91C_ADC_CDR5) & 0x3ff;
   for (i = 0; i
   break;
  }
}
}
}

3. Summary

Executing software reset of ADC will clear all ADC related registers, so it must be executed before setting ADC related registers.