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Why's conversion result obtained is swayed by the result conversion?

Latest Updated:02/01/2009

Question:

I made A/D conversion, switched successive analog inputs by ADS register.
But the conversion result thet obtained is influenced by the result conversion.
What was it caused?

Answer:

There are two cases.

(1) It is caused by Hardware.

  • Please lower the impedance of the signal source

Refer to the following chart for an example.


(2) It is caused by 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 order of the above.

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

Suitable Products
RL78 Family
78K Family
78K0/Dx
78K0/Fx
78K0/Ix
78K0/Kx
78K0/Lx
UPD78F07xx
UPD7800xx
UPD7802xx
UPD7803xx
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UPD7808xx
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UPD780xx
UPD78F8025
78K0/VAN ASCP