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epv
Joined: 23 Feb 2008
Posts: 8
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| bitbanging the ADS7822 12 bit serial ADC |
 Posted: Wed Feb 27, 2008 8:12 am |
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Having puzzled out this chip's weirdness, I thought others might find it useful. Seems to work fine. Loosely based on the ads8390 example code, but the 7822 operates differently.
| Code: |
#define ADS7822_CLK PIN_B4
#define ADS7822_DOUT PIN_B1
#define ADS7822_CS PIN_B3
void init_ext_adc()
{
output_high(ADS7822_CS);
output_high(ADS7822_CLK);
}
long read_ext_adc()
{
int i;
long data;
data=0;
output_low(ADS7822_CLK); // IMPORTANT!
output_low(ADS7822_CS); // CLK *must* drop just _before_ CS
delay_us(1);
output_high(ADS7822_CLK); // Start the conversion,
delay_us(1);
output_low(ADS7822_CLK); // and throw away the next
delay_us(1);
output_high(ADS7822_CLK); // three clocks, then you
delay_us(1);
output_low(ADS7822_CLK); // can collect the output
delay_us(1);
delay_us(1);
for(i=0;i<12;++i) { // Now we shift out valid data.
output_low(ADS7822_CLK);
delay_us(1);
shift_left(&data,2,input(ADS7822_DOUT));
output_high(ADS7822_CLK);
delay_us(1);
}
output_high(ADS7822_CS);
return(data);
}
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enzo84
Joined: 11 Jun 2011
Posts: 1
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| Re: bitbanging the ADS7822 12 bit serial ADC |
| Posted: Sat Jun 11, 2011 4:13 pm |
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Hi, epv, I tested this code using a PIC16F876 to read the ads7822, and it worked but I found a problem. The value received was half what it should be. Looking at your code and ads7822's datasheet I found that it lacked a rising edge, so I added that pulse and now the code worked well, got the expected value by reading the ADC. This works. The code is:
| Code: |
#define ADS7822_CLK PIN_B0
#define ADS7822_DOUT PIN_B1
#define ADS7822_CS PIN_B2
void init_ext_adc()
{
output_high(ADS7822_CS);
output_high(ADS7822_CLK);
}
long read_ext_adc()
{
int i;
long data;
data=0;
output_low(ADS7822_CLK); // IMPORTANT!
output_low(ADS7822_CS); // CLK *must* drop just _before_ CS
delay_us(1);
output_high(ADS7822_CLK); // Start the conversion,
delay_us(1);
output_low(ADS7822_CLK); // primer flanco descendente
delay_us(1);
output_high(ADS7822_CLK);
delay_us(1);
output_low(ADS7822_CLK); // segundo flanco descendente (bit nulo)
delay_us(1);
output_high(ADS7822_CLK); // <--- pulso que faltaba
delay_us(1); // en el próximo flanco descendente
//se obtiene el primer bit (msb)
for(i=0;i<12;++i) { // Now we shift out valid data.
output_low(ADS7822_CLK);
delay_us(1);
shift_left(&data,2,input(ADS7822_DOUT));
output_high(ADS7822_CLK);
delay_us(1);
}
output_high(ADS7822_CS);
return(data);
}
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Regards, Enzo. |
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