Renesas M16C Series

A-D Converter
M30240 Group
Rev.1.00 Sep 24, 2003 Page 248 of 360
2.6.4.2 A/D Conversion method, 8-bit mode
In 8-bit mode, the 8 higher-order bits of the 10-bit successive comparison register becomes the A-D
conversion result. Hence, if compared to a result obtained by using an 8-bit A-D converter, the voltage
compared is different by 3 Vref/2048 (see underscored in Table 2.33), and differences in stepping points
of output codes occur as shown in Figure 2.94.
Table 2.35: Comparison voltage of 8-bit mode to 8-bit A-D converter
Figure 2.94: Conversion level characteristics between 8-bit mode and 8-bit A-D converter
8-bit mode 8-bit A-D converter
Comparison voltage Vref
n = 0 0 0
n = 1 to 255
V
REF x n - VREF x 0.5
2
8
2
10
VREF x n - VREF x 0.5
2
8
2
8
07
05
06
03
00
02
Analog input voltage (mV)
Output code
(Result of A-D conversion)
02
01
00
Analog input voltage (mV)
Output code
(Result of A-D conversion)
04
02
01
00
01
10-bit
mode
8-bit
mode
8bit-mode
10bit-mode
08
09
10 30
17.5 37.5
(Note)
Optimal conversion characteristics of 8-bit A-D converter (V REF = 5.12 V)
Optimal conversion characteristics in 8-bit mode (V REF = 5.12 V)
Note: Differences in stepping points of output code for analog input voltage.