Hi all.
As says in datasheet on p.26, the adc values are coded in two-s complement. But my scheme is using unipolar signal (0 to 4.096V) for adc inputs.
I cant understand how to can convert the signed values to unipolar values? The values are always signed?
AINCOM is connected to VREFN and analog GND net.
So, for example, i read this values from ADC:
VCC = 10.66667v GAIN = 0.99503v REF = 10.66667v TEMP = 24.57360C OFFSET = 0.00334v 000000 AIN 0: 0.00000v 56c1d7 AIN 1: 3.17450v 56c118 AIN 2: 3.17439v 56c31a AIN 3: 3.17468v 56beee AIN 4: 3.17408v 56bee0 AIN 5: 3.17407v 004ef6 AIN 6: 0.01129v 5bd0b9 AIN 7: 3.35958v 5bca58 AIN 8: 3.35866v 5be632 AIN 9: 3.36264v 5bb8e8 AIN10: 3.35617v 5bad18 AIN11: 3.35448v 5b7166 AIN12: 3.34595v ff547b AIN13: 9.34267v 5b4752 AIN14: 3.33994v 5bc839 AIN15: 3.35836v
As you can see, for status bytes and AIN13 i have a invalid values. How treat this ADC codes correctly?
Please help. Thanks a lot.
Code that reads ADC:
#define SCALE (4.096 / 0x780000) * 1.06666660308837
#define V 1
#define mV 0.001
#define uV 0.000001
// read values in auto-scan mode
void adc_request_values(uint8_t n_channels)
{
uint8_t buf[16+5][4] = {0,0};
uint8_t ch, byte = 0;
float vcc, adcgain, ref, temp, offset = 0;
int32_t tmp = 0;
ADS_SET_HIGH(ADS_PIN_START); // start conversion
for(ch = 0; ch < n_channels+5; ch++)
{
while(GPIO_ReadInputDataBit(GPIOA, ADS_PIN_DRDY) != 0); // wait for data ready
// read data direct
ADS_SET_LOW(ADS_PIN_CS);
for(byte = 0; byte < 4; byte++)
{
buf[ch][byte] = ads_spi_xmit(0);
}
ADS_SET_HIGH(ADS_PIN_CS);
}
ADS_SET_LOW(ADS_PIN_START); // stop conversion
offset = ((uint32_t) ((buf[16][1] << 16) | (buf[16][2] << 8) | buf[16][3])) / 786432.0;
vcc = ((uint32_t) ((buf[17][1] << 16) | (buf[17][2] << 8) | buf[17][3])) / 786432.0;
temp = (((((uint32_t) ((buf[18][1] << 16) | (buf[18][2] << 8) | buf[18][3])) * SCALE * uV) - 168) / 394) + 25 ;
adcgain = ((uint32_t) ((buf[19][1] << 16) | (buf[19][2] << 8) | buf[19][3])) / 7864320.0;
ref = ((uint32_t) ((buf[20][1] << 16) | (buf[20][2] << 8) | buf[20][3])) / 786432.0;
printf("VCC = %2.5fv\n", vcc);
printf("GAIN = %2.5fv\n", adcgain);
printf("REF = %2.5fv\n", ref);
printf("TEMP = %2.5fC\n", temp);
printf("OFFSET = %2.5fv\n", offset);
printf("\n");
for(ch = 0; ch < n_channels; ch++)
{
printf("%06x", (uint32_t) ((buf[ch][1] << 16) | (buf[ch][2] << 8) | buf[ch][3]));
printf(" AIN%2d:", (buf[ch][0] & 0x1F) - 8);
printf(" %2.5fv", ((buf[ch][1] << 16) | (buf[ch][2] << 8) | buf[ch][3]) * SCALE / adcgain);
if(((buf[ch][0] & 0x40) >> 6) == 1) printf(" Voltage overflow! (Vin > 1.06*Vref)");
if(((buf[ch][0] & 0x20) >> 5) == 1) printf(" Lost supply! (AVDD-AVSS below a preset limit)");
printf("\n");
}
}
