The ADC module share VREFHI and
VREFLO inputs. In external reference mode, these pins are used as a ratiometric
reference to determine the ADC conversion input range.
See Section 12.12.4 for information on how to supply the reference voltage.
Note:
- On devices with no external
VREFHI and VREFLO pin, VREFHI is internally tied to VDDA and VREFLO is internally
connected to the device analog ground, VSSA.
Internal reference mode is not available for packages lacking VREFHI and
VREFLO pins. See the device data sheet for packages with VREFHI and
VREFLO pins available.
- To enable the external reference mode, the bit ANAREFSEL in register
REFCONFIGA from AnalogSubsysRegs must be set to 1
(AnalogSubsysRegs.REFCONFIGA.bit.ANAREFSEL = 1).
- See the device data sheet to
determine the allowable voltage range for VREFHI and VREFLO.
- The external reference mode
requires an external capacitor and resistor on the VREFHI pin. See the device data sheet
for the specific values required.