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AD7770 SPI MISO Always Gives 0x20

Question asked by zlassy on Mar 26, 2018
Latest reply on Jun 28, 2018 by jfigueroa

We are using an STM32 board to communicate with AD7770 using SPI. As shown in the attached picture, the MCU is providing the correct clock, MOSI, and CS. However, the ADC MISO is always 0x20, regardless of any changes. This is shown in the attached oscilloscope capture. 

 

We tried introducing a delay between CS and the clock/MOSI becomes always 0x81. 

 

Mode 3 pin (Alert_SPI) is always high, even if the MCU is not connected. 

 

VIO is set to 3.3V

and +12V is connected to a 12V power supply.

The SCK(shown in green) is 500.9kHZ

 

We have not made any modifications to the board, and left it in the Default SPI mode. 

 

MISO is Blue

MOSI is Purple

CS is Yellow 

Clk is Green

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