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15.5
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. The ADI interrupt request can be
designated as a DMAC activation source. In this case, an interrupt request is not sent to the CPU.
15.6
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 should be in the range AV
2. Relationships of AV
follows: AV
= V
SS
used.
3. V
Programming Range: The reference voltage input at the V
REF
≤ AV
V
.
REF
CC
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
to AN
0
like the one in figure 15.7 between AV
and V
and the filter capacitors connected to AN
REF
capacitors like the ones in figure 15.7 are connected, the voltage values input to the analog
input pins (AN
to AN
0
A/D conversion is 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.
≤ AN
SS
n
and AV
to V
and V
CC
SS
CC
. AV
and AV
must not be left open, even if the A/D converter is not
SS
CC
SS
to AN
), analog reference voltage (V
0
7
) should be connected to a stable digital ground (V
SS
) and analog reference voltage pin (V
7
CC
) will be smoothed, which may give rise to error. Error can also occur if
7
≤ V
.
REF
: AV
, AV
, V
SS
CC
SS
REF
and AV
. The bypass capacitors connected to AV
SS
to AN
must be connected to AV
0
7
Rev. 4.00 Jan 26, 2006 page 587 of 938
Section 15 A/D Converter
, and V
should be related as
CC
SS
pin should be in the range
REF
), and analog supply
REF
). The
SS
) at one point on the
SS
), connect a protection circuit
SS
REJ09B0276-0400
CC
. If filter
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