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Section 21 A/D Converter
21.6.4
Influences on Absolute Precision
Adding capacitance results in coupling with GND, and therefore noise in GND may adversely
affect absolute precision. Be sure to make the connection to an electrically stable GND such as
AVss.
Care is also required to insure that filter circuits do not communicate with digital signals on the
mounting board (i.e., acting as antennas).
21.6.5
Stop during A/D Conversion
When A/D conversion is stopped with a program during A/D conversion, see the following notes.
1. In single mode, A/D conversion cannot be stopped with a program during A/D conversion.
2. In multi mode or scan mode, when A/D conversion is stopped with a program during A/D
conversion, write 0 only to the ADST bit. If the ADST bit and the other bits are set
simultaneously, the operation of A/D conversion cannot be guaranteed.
3. In multi mode or scan mode, when A/D conversion is stopped during A/D conversion, write 0
to the ADST bit. And then the ADST bit is set 1 after the time which is longer than the A/D
conversion time has elapsed.
4. When the value of the ADST bit is changed, the period which is longer then one clock cycle
selected by the CKS[1:0] bits in ADCSR0 and ADCSR1 must be kept because the ADST bit is
sampling by the clock cycle selected by the setting of the CKS bits. If the period until the next
change of the ADST bit is shorter, that change may not be detected correctly.
Rev. 4.00 Sep. 14, 2005 Page 816 of 982
REJ09B0023-0400
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