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ADC: the bottom 3 bits of ADC output are always zero

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its a 12 bit ADC .... silly of me to think the bottom 3 bits are
valid!
This commit is contained in:
Andrew Tridgell 2011-09-15 23:03:24 +10:00
parent 812cd3562f
commit 2ae78e197e
1 changed files with 15 additions and 11 deletions
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26
libraries/AP_ADC/AP_ADC_ADS7844.cpp
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@ -84,25 +84,29 @@ ISR (TIMER2_OVF_vect)
ADC_SPI_transfer(adc_cmd[0]); // Command to read the first channel
for (ch = 0; ch < 8; ch++) {
uint16_t count = _count[ch];
uint32_t sum = _sum[ch];
uint16_t v;
if (++count == 0) {
v = ADC_SPI_transfer(0) << 8; // Read first byte
v |= ADC_SPI_transfer(adc_cmd[ch + 1]); // Read second byte and send next command
if (v & 0x8007) {
// this is a 12-bit ADC, shifted by 3 bits.
// if we get other bits set then the value is
// bogus and should be ignored
continue;
}
if (++_count[ch] == 0) {
// overflow ... shouldn't happen too often
// unless we're just not using the
// channel. Notice that we overflow the count
// to 1 here, not zero, as otherwise the
// reader below could get a division by zero
sum = 0;
count = 1;
_sum[ch] = 0;
_count[ch] = 1;
last_ch6_micros = micros();
}
_count[ch] = count;
sum += ADC_SPI_transfer(0) << 8; // Read first byte
sum += ADC_SPI_transfer(adc_cmd[ch + 1]); // Read second byte and send next command
_sum[ch] = sum;
_sum[ch] += (v >> 3);
}
bit_set(PORTC, 4); // Disable Chip Select (PIN PC4)