PD17012_15 Datasheet, PDF (154/320 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLERS WITH DIGITAL TUNING SYSTEM HARDWARE

µPD17012, 17P012
13.6.2 Successive approximation by binary search method
The A/D converter can compare only one voltage at one time.
To convert an input voltage into a digital signal, therefore, successive approximation must be executed by
program.
If the processing time of the successive approximation program differs depending on the input voltage, the
relationship with the other processing programs may be undesirable.
Therefore, use of the binary search method as explained in (1) through (3) below is recommended.
(1) Concept of binary search
The concept of binary search is explained below.
First, the compare voltage is set to 1/2 VDD. If the result of comparison is True (a high level is input), a voltage
of 1/4 VDD is added to the result; if the result of comparison is False (a low level is input), a voltage of 1/4 VDD
is subtracted from the result and compared.
Subsequently, the compare voltage is sequentially compared with 1/8 VDD and 1/16 VDD to 1/64 VDD. If the
result of comparison is False after comparison has been executed six times, 1/64 VDD is subtracted from the
result and comparison is completed.
1
H
Compare
voltage
1/2
(×VDD)
L
0
H
3/4
L
H
1/4
L
H
7/8
L
15/16
13/16
H
5/8
L
H
3/8
L
11/16
9/16
7/16
5/16
H
1/8
L
3/16
1/16
H
15/16
L
H
13/16
L
H
31/32
L
H
29/32
L
H
27/32
L
H
25/32
L
63/64
L
61/64
L
59/64
L
57/64
L
55/64
L
53/64
L
51/64
L
49/64
L
1
63/64
62/64
61/64
60/64
59/64
58/64
57/64
56/64
55/64
54/64
53/64
52/64
51/64
50/64
49/64
48/64
First
Second
Third Fourth
time
time
time
time
Fifth
Sixth
time
time
Subtracts 1/64
if False
152
Data Sheet U10101EJ4V0DS