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19.5
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.
19.6
Usage Notes
The following points should be noted when using the A/D converter.
Setting Range of Analog Power Supply and Other Pins:
1. Analog input voltage range
The voltage applied to the ANn analog input pins during A/D conversion should be in the
range AV
SS ≤ ANn ≤ AVCC (n = 0 to 7).
2. Digital input voltage range
The voltage applied to the CINn digital input pins should be in the range AV
SS ≤ CINn ≤
AV
CC and VSS ≤ CINn ≤ VCC (n = 0 to 7).
3. Relation between AV
CC, AVSS and VCC, VSS
As the relationship between AV
CC, AVSS and VCC, VSS, set AVSS = VSS. If the A/D converter is
not used, the AVCC and AVSS pins must on no account be left open.
If conditions 1 to 3 above are not met, the reliability of the device may be adversely affected.
Notes on Board Design: In board design, digital circuitry and analog circuitry should be as
mutually isolated as possible, and layout in which digital circuit signal lines and analog circuit
signal lines cross or are in close proximity should be avoided as far as possible. Failure to do so
may result in incorrect operation of the analog circuitry due to inductance, adversely affecting
A/D conversion values.
Also, digital circuitry must be isolated from the analog input signals (AN0 to AN7), and analog
power supply (AVCC) by the analog ground (AVSS). Also, the analog ground (AVSS) should be
connected at one point to a stable digital ground (VSS) on the board.
Notes on Noise Countermeasures: A protection circuit connected to prevent damage due to an
abnormal voltage such as an excessive surge at the analog input pins (AN0 to AN7) should be
connected between AVCC and AVSS as shown in figure 19.7.
Also, the bypass capacitors connected to AVCC and the filter capacitor connected to AN0 to
AN7 must be connected to AVSS.
If a filter capacitor is connected as shown in figure 19.7, the input currents at the analog input
pins (AN0 to AN7) are averaged, and so an error may arise. Also, when A/D conversion is
performed frequently, as in scan mode, if the current charged and discharged by the capacitance