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M30245 Group
2.9.8 Precautions for A/D Converter
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Figure 2.9.17. Use of capacitors to reduce noice
Rev.2.00 Oct 16, 2006
REJ09B0340-0200
(1) Write to each bit (except bit 6) of AD control register 0, to each bit of AD control register 1, and
to bit 0 of AD control register 2 when A/D conversion is stopped (before a trigger occurs).
In particular, when the Vref connection bit is changed from 0 to 1, start A/D conversion after
an elapse of 1 µs or longer.
(2) To reduce conversion error due to noise, connect a voltage to the AVcc pin and to the Vref pin from
an independent source. It is recommended to connect a capacitor between the AVss pin and the
AVcc pin, between the AVss pin and the Vref pin, and between the AVss pin and the analog input
pin (ANi). Figure 2.9.17 shows the an example of connecting the capacitors to these pins.
Microcomputer
V
CC
AV
CC
V
REF
C1
AV
SS
C3
AN
i
(3) Set the direction register of the following ports to input: the port corresponding to a pin to be
used as an analog input pin and external trigger input pin (P9
(4) Rewrite to analog input pin after changing A/D operation mode.
(5) When using the one-shot or single sweep mode
Confirm that A/D conversion is complete before reading the AD register.
(Note: When A/D conversion interrupt request bit is set, it shows that A/D conversion is completed.)
(6) When using the repeat mode or repeat sweep mode 0 or 1
Use the undivided main clock as the internal CPU clock.
(7) In using a key-input interrupt, none of the 8 pins (AN
conversion port (if the A/D input voltage goes to "L" level, a key-input interrupt occurs).
(8) Use φAD under 10 MHz. When X
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C2
Note
1:
C1≥0.47 µF, C2≥0.47 µF, C3≥100 pF
(for reference)
Use thick and shortest possible wiring
Note
2:
to connect capacitors.
is over 10 MHz, divide it.
IN
2. A/D Converter
).
3
through AN
) can be used as an A/D
0
7
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