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External Analog Reference Voltage KEAZ128(80LQFP)

Question asked by Bence Kovari on Oct 6, 2016
Latest reply on Oct 9, 2016 by Bence Kovari

Hi, my name is Bence Kovari from Hungary. I have an FRDM-KEAZ128 board (80 LQFP package). Iam doing ADC, and i would like to use an External Voltage source as Analog Reference. The way i tried: I've checked my Header/Pinout, and connected my own voltage (in this case 1V) to AREF pin, and gnd to gnd (just one pin below AREF).  I coded the initialization structure, ADC_Init() etc (works fine so far). I add the line to the code to select  external VREF: 

 

 

ADC_VrefSelect(ADC,0x01);

 

Then i read the channel ADC_CHANNEL_AD29_VREFH that should show my own external voltage,

but nothing happens. It's still 5V, the internal ref regardless. I've also tried:

 

ADC_SC2 |=ADC_SC2_REFSEL(0b01); (which i copied from an example source code).

 

I've checked the Reference manual that describes this topic quite shortly and messy a bit. Or i may have misunderstood something in the vref schematics or channel/pins description. So please if you could tell me how to do this stuff correctly i would really appreciate that!

 

Sincerely,
B.K.

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