Renesas M16C FAMILY, User Manual

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Rev.2.00 Oct 16, 2006 page 231 of 354
REJ09B0340-0200
M30245 Group 2. A/D Converter
Successive approximation register : n
Vref (V)
x –
1024
V
REF
2048
V
REF
n
0 0
1 to1023
(1) The A/D converter compares the reference voltage (Vref) generated internally based on the
contents of the successive comparison register with the analog input voltage (V
IN
) input from
the analog input pin. The comparison result is stored in the successive comparison register
and then V
IN
is converted to digital value (successive comparison method). If a trigger oc-
curs, the A/D converter carries out the following:
1. Fixes bit 9 of the successive comparison register.
Compares Vref with V
IN
: [In this instance, the contents of the successive comparison
register are “1000000000
2
” (default).]
Bit 9 of the successive comparison register varies depending on the comparison re-
sult as follows.
If Vref < V
IN
, then “1” is assigned to bit 9.
If Vref > V
IN
, then “0” is assigned to bit 9.
2. Fixes bit 8 of the successive comparison register.
Sets bit 8 of the successive comparison register to “1”, then compares Vref with V
IN
.
Bit 8 of the successive comparison register varies depending on the comparison
result as follows:
If Vref < V
IN
, then “1” is assigned to bit 8.
If Vref > V
IN
, then “0” is assigned to bit 8.
3. Fixes bit 7 through bit 0 of the successive comparison register.
Carries out step 2 above on bit 7 through bit 0.
After bit 0 is fixed, the contents of the successive comparison register (conversion
result) are transmitted to AD register i.
Vref is generated based on the latest content of the successive comparison register. Table
2.9.8 shows the relationship of the successive comparison register contents and Vref. Table
2.9.9 shows how the successive comparison register and Vref vary while A/D conversion is in
progress. Figure 2.9.18 shows theoretical A/D conversion characteristics.
2.9.9 Method of A/D Conversion (10-bit mode)
Table 2.9.8. Relationship of the successive comparison register contents and Vref