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ADS8685: Can't read out the data correctly

user5074321
Prodigy 20 points
Part Number: ADS8685

hello,

I hava tried to send 

Frame 1) Write Command

Drop CS and issue write command:

D024 5555

Raise CS

Frame 2) Read Command

Drop CS and issue read command:

C824 0000

Raise CS

Frame 3) Read Register Value

Drop CS, but do not provide any commands on the MOSI

0000 0000

Raise CS

The result is 5555,that's right.

Then I tried to test. Firstly I send D014 0008 to make 0 to 12.288V

Then I tried to send only 0000 0000 to read out the ad value,all I get were not what I expect.I measured the voltage,1.8V. But the read result is 0x0581. 

If I do not send D014 0008 ,after send 00000000, the result is 0x86d3 when 1.8v,0x6300 when 0v.

I'm not sure what was wrong.I need some help,thanks.

  • 0
    TI__Expert 3175 points
    Hi,

    All of the codes that you mention are correct, but I agree that the read results are not correct. Can you please send a screenshot of the frame when you program the input range register (D014 0008) as well as the next frame (0000 0000), with a 1.8V input as well as with a 0V input?

    Have you configured any other registers?

    You are using the internal voltage reference, correct?

    Do you have anything in the front end that would pull the input up or down? If you can share your input circuit, that would be helpful.
  • 0 in reply to Evan Sawyer
    Prodigy 20 points
    Something was wrong with the circuit board and the voltage I measured was a wave.The program is correct.
    Thanks a lot.