RFM31 Datasheet, PDF (43/137 Pages) –

RFM31
8.3. General Purpose ADC
An 8-bit SAR ADC is integrated onto the module for general purpose use, as well as for digitizing the temperature
sensor reading. ―Register 0Fh. ADC Configuration,‖ must be configured depending on the use of the GP ADC before
use. The architecture of the ADC is demonstrated in Figure 18. First the input of the ADC must be selected by setting
the ADCSEL[2:0] depending on the use of the ADC. For instance, if the ADC is going to be used to read out the
internal temperature sensor, then ADCSEL[2:0] should be set to 000. Next, the input reference voltage to the ADC
must be chosen. By default, the ADC uses the bandgap voltage as a reference so the input range of the ADC is from
0–1.02 V with an LSB resolution of 4 mV (1.02/255). Changing the ADC reference will change the LSB resolution
accordingly.
Every time the ADC conversion is desired, the ADCStart bit in ―Register 0Fh. ADC Configuration,‖ must be set to 1.
This is a self clearing bit that will be cleared at the end of the conversion cycle of the ADC. The conversion time for
the ADC is 350 us. After the 350 us or when the ADCstart/busy bit is cleared, then the ADC value may be read out of
"Register 11h. ADC Value". Setting the "Register 10h. ADC Sensor Amplifier Offset", ADC Sensor Amplifier Offset is
only necessary when the ADC is configured to used as a Bridge Sensor as described in the following section.
Figure 18. General Purpose ADC Architecture
Add R/W
0F R/W
10 R/W
11 R
Function/D
escription
ADC
Configuration
ADC Sensor
Amplifier Offset
ADC Value
D7
adcstart/ad
cbusy
adc[7]
D6
adcsel
[2]
adc[6]
D5
D4
D3
D2
adcsel
[1]
adc[5]
adcsel
[0]
adc[4]
adcref[1]
adcoffs[3
]
adc[3]
adcref[0]
adcoffs[
2]
adc[2]
D1
adcgain[1]
adcoffs[1]
adc[1]
D0
adcgain[0]
adcoffs[0]
adc[0]
POR
Def.
00h
00h
—
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