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14.5
Interrupts
The A/D converter generates an interrupt (ADI) at the end of A/D conversion. The ADI interrupt
request can be enabled or disabled by the ADIE bit in ADCSR.
14.6
Usage Notes
When using the A/D converter, note the following points:
1. Analog Input Voltage Range
During A/D conversion, the voltages input to the analog input pins AN
≤ AN
≤ V
AV
SS
n
2. Relationships of AV
AV
, AV
, V
CC
SS
CC
be left open, even if the A/D converter is not used.
3. V
Programming Range
REF
The reference voltage input at the V
4. Note on Board Design
In board layout, separate the digital circuits from the analog circuits as much as possible.
Particularly avoid layouts in which the signal lines of digital circuits cross or closely approach
the signal lines of analog circuits. Induction and other effects may cause the analog circuits to
operate incorrectly, or may adversely affect the accuracy of A/D conversion.
The analog input signals (AN
voltage (AV
) must be separated from digital circuits by the analog ground (AV
CC
analog ground (AV
board.
5. Note on Noise
To prevent damage from surges and other abnormal voltages at the analog input pins (AN
AN
) and analog reference voltage pin (V
7
14.7 between AV
capacitors connected to AN
ones in figure 14.7 are connected, the voltage values input to the analog input pins (AN
AN
) will be smoothed, which may give rise to error. Error can also occur if A/D conversion is
7
frequently performed in scan mode so that the current that charges and discharges the capacitor
in the sample-and-hold circuit of the A/D converter becomes greater than that input to the
analog input pins via input impedance (Rin). The circuit constants should therefore be selected
carefully.
412
.
REF
and AV
to V
CC
SS
, and V
should be related as follows: AV
SS
REF
to AN
0
) should be connected to a stable digital ground (V
SS
and AV
. The bypass capacitors connected to AV
CC
SS
to AN
0
7
and V
CC
SS
pin should be in the range V
), analog reference voltage (V
7
), connect a protection circuit like the one in figure
REF
must be connected to AV
should be in the range
n
= V
. AV
and AV
SS
SS
CC
≤ AV
.
REF
CC
), and analog supply
REF
) at one point on the
SS
and V
CC
. If filter capacitors like the
SS
must not
SS
). The
SS
to
0
and the filter
REF
to
0
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