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CHAPTER 10 8-BIT A/D CONVERTER (
µ
PD789426 AND 789446 SUBSERIES)
User’s Manual U15075EJ2V1UD
194
Figure 10-4. Basic Operation of 8-Bit A/D Converter
Conversion
time
Sampling
time
Sampling
A/D conversion
Undefined
Conversion
result
Conversion
result
A/D converter
operation
SAR
ADCR0
INTAD0
80H
C0H
or
40H
A/D conversion continues until bit 7 (ADCS0) of A/D converter mode register 0 (ADM0) is reset (0) by software.
If an attempt is made to write to ADM0 or analog input channel specification register 0 (ADS0) during A/D
conversion, the ongoing A/D conversion is canceled. In this case, A/D conversion is restarted from the beginning, if
ADCS0 is set (1).
RESET input makes A/D conversion result register 0 (ADCR0) undefined.
10.4.2 Input voltage and conversion result
The relationships between the analog input voltage at the analog input pins (ANI0 to ANI5) and the A/D
conversion result (A/D conversion result register 0 (ADCR0)) are represented by:
ADCR0 = INT (
×
256 + 0.5)
or
(ADCR0
−
0.5)
×
≤
V
IN
< (ADCR0 + 0.5)
×
INT( ):
Function that returns the integer part of a parenthesized value
V
IN
:
Analog input voltage
AV
DD
:
Supply voltage for the A/D converter
ADCR0: Value in A/D conversion result register 0 (ADCR0)
Figure 10-5 shows the relationship between the analog input voltage and the A/D conversion result.
V
IN
AV
DD
AV
DD
256
AV
DD
256
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