AREF for ADC in STK600-RCUC3A100-28(AT32UC3A1512)

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Dear,

 

I have been having issues with getting correct data transfer between a custom board (using AT32UC3A1512 mcu with USART and ADC on two channels) and a Raspberry Pi microcomputer. I wouldn't know if the A/D is done correctly nor if the data is transferred accurately as I observed that calculated/expected data is usually lower than received data on the RPi.

 

To this I was suggested to try other devices. Hence, I am using a STK600 and the RCUC3A100-28 routing card which has same mcu as the AT32UC3A1512. For this setup, I am sending in a known signal to be received by a MATLAB script using the RS232 Spare to RS232 cable to my PC's COM port. Data arriving on the MATLAB is all 1's (or 255) and my troubleshooting on the STK600 shows that there is no reference voltage on the AREF0 and AREF1 jumpers nor on the AREF0 and AREF1 AUX pins.

 

Could this mean I have to supply external reference voltages to the AREF0/1 pins or jumpers? Please advise.

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The UC3A1xxx does not have any internal voltage references for its' ADC, therefore you will need to supply an external reference voltage.
From my reading of the docs on that routing card and the STK600 it appears that ADVREF is connected to AREF0 and VDDANA is connected to VTG.
VTG (the main supply to the micro) should be between 3.0 and 3.6 volts.
ADVREF should be between 2.6 and VDDANA volts.

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Thanks @mikech,

 

I got under the hood and found that the I did not set Aref0/1 values on the STK600 in the Atmel Studio. My VTG was 3.2V, and I set Aref0/1 to 2.8V. Issues resolved and I did not need use External Vref.

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