C8051F960-B-GM Datasheet, PDF (84/492 Pages) Silicon Laboratories – Ultra Low Power 128K, LCD MCU Family

C8051F96x
5.3. 8-Bit Mode
Setting the ADC08BE bit in register ADC0CF to 1 will put the ADC in 8-bit mode.In 8-bit mode, only the
8 MSBs of data are converted, allowing the conversion to be completed in two fewer SAR clock cycles
than a 10-bit conversion. This can result in an overall lower power consumption since the system can
spend more time in a low power mode. The two LSBs of a conversion are always 00 in this mode, and the
ADC0L register will always read back 0x00.
5.4. 12-Bit Mode
C8051F96x devices have an enhanced SAR converter that provides 12-bit resolution while retaining the
10- and 8-bit operating modes of the other devices in the family. When configured for 12-bit conversions,
the ADC performs four 10-bit conversions using four different reference voltages and combines the results
into a single 12-bit value. Unlike simple averaging techniques, this method provides true 12-bit resolution
of ac or dc input signals without depending on noise to provide dithering. The converter also employs a
hardware Dynamic Element Matching algorithm that reconfigures the largest elements of the internal DAC
for each of the four 10-bit conversions to cancel the any matching errors, enabling the converter to achieve
12-bit linearity performance to go along with its 12-bit resolution. For best performance, the Low Power
Oscillator should be selected as the system clock source while taking 12-bit ADC measurements.
The 12-bit mode is enabled by setting the AD012BE bit (ADC0AC.7) to logic 1 and configuring Burst Mode
for four conversions as described in Section 5.2.3. The conversion can be initiated using any of the meth-
ods described in Section 5.2.1, and the 12-bit result will appear in the ADC0H and ADC0L registers. Since
the 12-bit result is formed from a combination of four 10-bit results, the maximum output value is 4 x (1023)
= 4092, rather than the max value of (2^12 – 1) = 4095 that is produced by a traditional 12-bit converter. To
further increase resolution, the burst mode repeat value may be configured to any multiple of four conver-
sions. For example, if a repeat value of 16 is selected, the ADC0 output will be a 14-bit number (sum of
four 12-bit numbers) with 13 effective bits of resolution.
84
Rev. 1.0