33.4.2.4 Output Formats

A single-ended conversion measures one input voltage against ground. The result of an n-bit single-ended conversion is an unsigned (positive) integer between 0 and the maximum value 2ⁿ - 1:

$RESULT\in \mathbb{Z}:0\le RESULT\le 2^n-1$

The result of an n-bit single-ended conversion, as provided in the Result (RESULT) register, is given by the following equation:

$RESULT=\frac{V_{INP}}{V_{REF}}\times 2^n$

A differential conversion measures the difference between two input voltages. The result of an n-bit differential conversion is a signed (positive or negative) integer between -2^{n - 1} and 2^{n - 1} - 1:

$RESULT\in \mathbb{Z}:{-2}^{n-1}\le RESULT\le 2^{n-1}-1$

The result of an n-bit differential conversion, as provided in the Result (RESULT) register, is given by the following equation:

$RESULT=\frac{V_{INP}-V_{INN}}{V_{REF}}\times 2^{n-1}$

Single-ended conversions are represented as unsigned values, while differential conversions use signed values in two’s complement form. When the conversion result does not occupy the whole register, the unused bits are set to ‘0’. However, for differential conversion results, the unused bits to the left of the result replicate the sign bit. This process, known as sign extension, ensures that the value retains its correct positive or negative sign when interpreted as a larger bit-width number.

The ADC has two output registers: The Sample (SAMPLE) and Result (RESULT) registers. The SAMPLE register is always updated with the latest ADC conversion output (one sample). In series and burst accumulation modes, samples are added together in an internal sample accumulator, which is configured by the Sample Accumulation Number Select bit field in the Control D register (CTRLD.SAMPNUM). The accumulated result is automatically transferred to the RESULT register when all samples are completed. In single conversion modes, the RESULT register is updated with the latest sample, making it identical to the SAMPLE register.

The Result Scaling bit field in the Control D register (CTRLD.SCALING) determines how data are presented in the SAMPLE and RESULT registers, as shown in the following table.

The data format for a single-ended conversion sample is an unsigned number, where 0x0000 represents zero and 0x0FFF represents the largest value (full scale). For differential conversions, the data format is two's complement with sign extension.

The following tables show the RESULT register output formats for single-ended and differential conversions, based on mode of operation, scaling, and resolution.