NEC mPD789101, User Manual

Page: 141 / 265

CHAPTER 11 8-BIT A/D CONVERTER (
µ
PD789104, 789124 SUBSERIES)
User’s Manual U13045EJ2V0UM00
141
Figure 11-4. Basic Operation of 8-Bit A/D Converter
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 A/D input select register 0 (ADS0) during A/D conversion, the ongoing
A/D conversion is canceled. In this case, if ADCS0 is set (1), A/D conversion is restarted from the beginning.
RESET input makes the A/D conversion result register 0 (ADCR0) undefined.
11.4.2 Input voltage and conversion result
The relationships between the analog input voltage at the analog input pins (ANI0 to ANI3) 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
: A/D converter supply voltage
ADCR0: Value in the A/D conversion result register 0 (ADCR0)
Figure 11-5 shows the relationships between the analog input voltage and the A/D conversion result.
AV
DD
256
V
IN
AV
DD
AV
DD
256
Conversion
time
Sampling
time
Sampling A/D conversion
Undefined
80H
C0H
or 40H
Conversion
result
Conversion
result
A/D converter
operation
SAR
ADCR0
INTAD0