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regarding adc vref for Tiva™ TM4C1294NCPDT Microcontroller

ANAND MOHAN
Prodigy 10 points
Other Parts Discussed in Thread: TM4C1294NCPDT

#define ADC_REF_INT             0x00000000  // Internal reference
#define ADC_REF_EXT_3V          0x00000001  // External 3V reference
#define ADC_REF_EXT_1V          0x00000003  // External 1V reference             

As per adc.h file for adc driver for the  Tiva™ TM4C1294NCPDT Microcontroller,these values are defined as vref value setting options.

if we relate this to data sheet for ADC Control (ADCCTL), offset 0x038, we set VREF bit as 1 for ADC_REF_EXT_3V and reset VREF bit as 0  for ADC_REF_INT.


how do we derive the logic for ADC_REF_EXT_1V .

 

  • 0
    Guru 47900 points

    ANAND MOHAN said:
    how do we derive the logic for ADC_REF_EXT_1V .

    Perhaps that's NOT the best idea!     Recently - right here - arrived a near identical posting.   

    These mixed signal devices are (mostly) unable to harvest (real) benefits doing as you suggest.     And - a good read of the MCU manual should alert you to the maker's bias against "so low" a VRef.

    Should you comply w/the MCU manual's direction - and seek a more "spec compliant" external VRef - that is achieved by setting bit 0 to 1 - and introducing a very proper VRef (signal & level) upon VRefA+ and GndA.

    If I may - if your candidate signal is too low in value to fully exercise the MCU's ADC signal input range - op-amps have classically "gained up" the signal.   One suspect - with facts in evidence (i.e. few) - that's your best bet...

  • 0 in reply to cb1
    TI__Guru**** 244400 points
    Hello Anand, cb1,

    That is an incorrect entry in the driverlib file. It should have been EXT and INT only. I have filed a bug request for correction

    Regards
    Amit