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What's the cause of the interferrencing of conversion results when swhitching analog inputs?

Last Updated:12/26/2017

Question:

I created an A/D conversion, and switched successive analog inputs by ADS register.
However, the conversion result that obtained is influenced by the result conversion.
What was the cause of this?

Answer:

There are two possible causes:

(1) It is caused by the hardware.

Please lower the impedance of the signal source.

Refer to the following chart for an example.


(2) It is caused by the software.
It causes by bad read-out timing the data of the conversion result.
Refer to the following for a program:
[1] Clear ADCS bit and stop A/D conversion operation
[2] Set ADMK bit and prohibit A/D interruption.
(During interrupt function execution, it is needless to prohibit)
[3] Clear ADIF bit.
[4] Switch the input by ADS register.
[5] Clear ADMK bit, and enable A/D interruption.
(During interrupt function execution it is needless to prohibit [5])
[6] Set up ADCS bit, and start to convert.
[7] Read-out the conversion data with A/D interruption.
We convert in the above order.

If you can't solve the problem by the methods mentioned above, please lengthen the time interval of each A/D conversion.

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