65.6.10.1 Input-output Transfer Functions

The ADC can be configured to operate in the following input voltage modes:

  • Single-ended—ADC_COR.DIFFx = 0. This is the default mode after a reset.
  • Differential—ADC_COR.DIFFx = 1 (see the figure below). In Differential mode, the ADC requires differential input signals having a VDD/2 common mode voltage (refer to section “Electrical Characteristics”).

The following equations give the unsigned ADC input-output transfer function in each mode(1). With signed conversions (see field ADC_EMR.SIGNMODE), subtract 2047 from the ADC_LCDR.DATA value given below.

In the formula, REFP = VREFP, REFN = VREFN.

Single-ended mode:

ADC_LCDR.LDATA = ADx − REFN REFP − REFN × 2 12

Differential mode:

ADC_LCDR.LDATA = 1 + ADx − ADx+1 REFP − REFN × 2 11
Note: Equations assume ADC_EMR.OSR = 1

If ADC_MR.ANACH is set, the ADC can manage both differential channels and single-ended channels. If ADC_MR.ANACH is cleared, the parameters defined in ADC_COR are applied to all channels.

The following table give s the internal positive and negative ADC inputs assignment with respect to the programmed mode (ADC_COR.DIFFx).

For example, if Differential mode is required on channel 0, input pins AD0 and AD1 are used. In this case, only channel 0 must be enabled by writing a 1 to ADC_CHER.CH0.

Table 65-2. Input Pins and Channel Numbers
Input Pin Channel Number
Single-ended Mode Differential Mode
AD0 CH0 CH0
AD1 CH1
AD2 CH2 CH2
AD3 CH3
AD4 CH4 CH4
AD5 CH5
AD6 CH6 CH6
AD7 CH7
AD8 CH8 CH8
AD9 CH9
AD10 CH10 CH10
AD11 CH11
Figure 65-7. Analog Full Scale Ranges in Single-Ended/Differential Applications