Rev. 5.00, 09/03, page 632 of 760
111
110
101
100
011
010
001
0000 1/8 2/8 3/8 4/8 5/8 6/8 7/8 FS
Analog input
voltage
FS: Full-scale voltage
(3) Quantization
error
Ideal A/D
conversion
characteristic
(4) Nonlinearity
error
Ideal A/D
conversion
characteristic
Actual A/D
convertion
characteristic
(2) Full-scale erro
r
Digital output
Analog input
voltage
(1) Offset error
FS
Digital output
Figure 20.8 Definitions of A/D Conversion Accuracy
20.7 Usage Notes
When using the A/D converter, note the following points.
20.7.1 Setting Analog Input Volt age
• Analog Input Voltage Range: During A/D conversion, the voltages input to the analog input
pins ANn should be in the range AVSS ≤ ANn ≤ AVCC (n = 0 to 7).
• Rela tionships of AVCC and AVSS: AVCC and AVSS should be related as follows: AVCC =
VCC ± 0.3 V and AVSS = VSS.
20.7.2 Processing of Analog Input Pins
To pre vent da mage fr o m volt age sur ge s at the ana l og input pi ns (AN0 to AN7), connect an input
protection circuit like the one shown in figure 20.9. The circuit shown also includes an CR filter to
suppress noise. Thi s c ircuit is shown as an example; the ci rcuit constants shou ld be s elected
according to actual application conditions. Table 20.5 lists the analog input pin specifications and
figure 20.10 shows an equivalent circuit diagram of the analog input ports.