m37905 Renesas Electronics Corporation., m37905 Datasheet - Page 327

• Manufacturer Part Number: m37905
• Description: Mitsubishi 16-bit Single-chip Microcomputer 7700 Family / 7900 Series
• Manufacturer: Renesas Electronics Corporation.

A-D CONVERTER
12.3 A-D conversion method
12.3 A-D conversion method
The A-D converter compares the comparison voltage (V
contents of the successive approximation register, with the analog input voltage (V
the analog input pin (AN
is converted into a digital value. When a trigger is generated, the A-D converter performs the following
processing:
V
the relationship between the successive approximation register’s contents and V
list the changes of the successive approximation register and V
Figure 12.3.1 shows the ideal A-D conversion characteristics in the 10-bit resolution mode.
12-16
ref
is generated according to the latest contents of the successive approximation register. Table 12.3.1 lists
Determining bit 9 of the successive approximation register
Determining bit 8 of the successive approximation register
Determining bits 7 to LSB of the successive approximation register
The A-D converter compares V
register is “1000000000
Bit 9 of the successive approximation register depends on the comparison result as follows:
After setting bit 8 of the successive approximation register to “1,” the A-D converter compares V
V
Operation
Operation
When the LSB is determined, the contents of the successive approximation register (in order words,
conversion result) are transferred to the A-D register i.
IN
When V
When V
When V
When V
. Bit 8 depends on the comparison result as follows:
ref
ref
ref
ref
< V
> V
< V
> V
is performed for each of bits 7 to 0 in the 10-bit resolution mode.
is performed for each of bits 7 to 2 in the 8-bit resolution mode.
IN
IN
IN
IN
, bit 9 = “1”
, bit 9 = “0”
, bit 8 = “1”
, bit 8 = “0”
Table 12.3.1 Relationship between successive approximation register’s contents and V
V
i
). By reflecting the comparison result on the successive approximation register, V
REF
Successive approximation register’s contents: n
: Reference voltage
2
” (initial value).
ref
with V
7905 Group User’s Manual Rev.1.0
1 to 1023
0
IN
. At this time, the contents of the successive approximation
ref
), which is internally generated according to the
ref
during the A-D conversion, respectively.
1024
V
ref
REF
. Tables 12.3.2 and 12.3.3
V
IN
ref
), which is input from
0
(V)
(n – 0.5)
ref
with
IN
ref