7702 Datasheet, PDF (228/522 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER

A-D CONVERTER
8.3 A-D conversion method
8.3 A-D conversion method
The A-D converter compares the comparison voltage (Vref), which is internally generated according to the
contents of the successive approximation register, with the analog input voltage (VIN), which is input from
the analog input pin (ANi). By reflecting the comparison result on the successive approximation register, VIN
is converted into a digital value. When a trigger is generated, the A-D converter performs the following
processing:
ΠDetermining bit 7 of the successive approximation register
The A-D converter compares Vref with VIN. At this time, the contents of the successive approximation
register is “100000002” (initial value).
Bit 7 of the successive approximation register changes according to the comparison result as follows:
When Vref < VIN, bit 7 = “1”
When Vref > VIN, bit 7 = “0”
 Determining bit 6 of the successive approximation register
After setting bit 6 of the successive approximation register to “1,” the A-D converter compares Vref
with VIN. Bit 6 changes according to the comparison result as follows:
When Vref < VIN, bit 6 = “1”
When Vref > VIN, bit 6 = “0”
Ž Determining bits 5 to 0 of the successive approximation register
Operations in  are performed for bits 5 to 0.
When bit 0 is determined, the contents (conversion result) of the successive approximation register
is transferred to the A-D register i.
The comparison voltage (Vref) is generated according to the latest contents of the successive approximation
register. Table 8.3.1 lists the relationship between the successive approximation register’s contents and Vref.
Table 8.3.2 lists changes of the successive approximation register and Vref during the A-D conversion. Figure
8.3.1 shows the ideal A-D conversion characteristics.
Table 8.3.1 Relationship between successive approximation register’s contents and Vref
Successive approximation register’s contents: n
Vref (V)
0
0
1 to 255
VV
REF
256
! (n – 0.5)
VREF^V: Reference voltage
8–10
7702/7703 Group User’s Manual