
1.7 Precautions for A-D Converter
20
Mitsubishi microcomputers
M16C / 62P Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
development
Preliminary Specifications Rev.1.0
Specifications in this manual are tentative and subject to change.
1.7 Precautions for A-D Converter
1. Set ADCON0 (except bit 6), ADCON1 and ADCON2 registers when A-D conversion is stopped (before
a trigger occurs).
2. When the VCUT bit of ADCON1 register is changed from
“
0
”
(Vref not connected) to
“
1
”
(Vref con-
nected), start A-D conversion after passing 1
μ
s or longer.
3. To prevent noise-induced device malfunction or latchup, as well as to reduce conversion errors, insert
capacitors between the AV
CC
, V
REF
, and analog input pins (ANi) each and the AV
SS
pin. Similarly,
insert a capacitor between the V
CC
pin and the V
SS
pin. Figure 1.7.1 is an example connection of each
pin.
4. Make sure the port direction bits for those pins that are used as analog inputs are set to
“
0
”
(input
mode). Also, if the ADCON0 register
’
s TGR bit = 1 (external trigger), make sure the port direction bit for
the AD
TRG
pin is set to
“
0
”
(input mode).
5.
When using key input interrupts, do not use any of the four AN
4
to AN
7
pins as analog inputs. (A key
input interrupt request is generated when the A-D input voltage goes low.)
6. The
φ
AD
frequency must be 10 MHz or less. Without sample-and-hold function, limit the
φ
AD
frequency
to 250kH
Z
or more. With the sample and hold function, limit the
φ
AD
frequency to 1MH
Z
or more.
7. When changing an A-D operation mode, select analog input pin again in the CH2 to CH0 bits of
ADCON0 register and the SCAN1 to SCAN0 bits of ADCON1 register.
Figure 1.7.1. Use of capacitors to reduce noise
Microcomputer
Note 1: C1
≥
0.47
μ
F, C2
≥
0.47
μ
F, C3
≥
100pF, C4
≥
0.1
μ
F, C5
≥
0.1
μ
F (reference)
Note 2: Use thick and shortest possible wiring to connect capacitors.
V
CC1
V
SS
AV
CC
AV
SS
V
REF
ANi
C4
C1
C2
C3
V
CC2
V
SS
C5
ANi: ANi, AN
0
i, and AN
2
i (i=0 to 7)