CHAPTER 12 A/D CONVERTER
User’s Manual U16899EJ2V0UD
256
12.4.2 Input voltage and conversion results
The relationship between the analog input voltage input to the analog input pins (ANI0 to ANI7) and the theoretical
A/D conversion result (stored in the A/D conversion result register (ADCR)) is shown by the following expression.
SAR = INT (
×
1024 + 0.5)
ADCR = SAR × 64
or
(ADCR
−
0.5)
×
≤
V
AIN
< (ADCR + 0.5)
×
where, INT( ): Function which returns integer part of value in parentheses
V
AIN
:
Analog input voltage
AV
REF
: AV
REF
pin voltage
ADCR: A/D conversion result register (ADCR) value
SAR:
Successive approximation register
Figure 12-10 shows the relationship between the analog input voltage and the A/D conversion result.
Figure 12-10. Relationship Between Analog Input Voltage and A/D Conversion Result
1023
1022
1021
3
2
1
0
FFC0H
FF80H
FF40H
00C0H
0080H
0040H
0000H
A/D conversion result
(ADCR)
SAR
ADCR
1
2048
1
1024
3
2048
2
1024
5
2048
Input voltage/AV
REF
3
1024
2043
2048
1022
1024
2045
2048
1023
1024
2047
2048
1
V
AIN
AV
REF
AV
REF
1024
AV
REF
1024