115
A-D converter
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6
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Item
Performance
Method of A-D conversion
Analog input voltage (Note 1) 0V to AV
CC
(V
CC
)
Operating clock
φ
AD
(Note 2) V
CC
= 5V
Successive approximation (capacitive coupling amplifier)
f
AD
/divide-by-2 of f
AD
/divide-by-4 of f
AD
, f
AD
=f(X
IN
)
divide-by-2 of f
AD
/divide-by-4 of f
AD
, f
AD
=f(X
IN
)
8-bit or 10-bit (selectable)
V
CC
= 5V
Without sample and hold function
±
3LSB
With sample and hold function (8-bit resolution)
±
2LSB
Without sample and hold function (10-bit resolution)
±
3LSB
V
CC
= 3V
Without sample and hold function (8-bit resolution)(Note 3)
±
2LSB
One-shot mode, repeat mode, single sweep mode, repeat sweep mode 0,
and repeat sweep mode 1
8pins (AN
0
to AN
7
)
A-D conversion start condition
Software trigger
A-D conversion starts when the A-D conversion start flag changes to “1”
Conversion speed per pin
Without sample and hold function
8-bit resolution: 49
φ
AD
cycles, 10-bit resolution: 59
φ
AD
cycles
With sample and hold function
8-bit resolution: 28
φ
AD
cycles, 10-bit resolution: 33
φ
AD
cycles
Note 1: Does not depend on use of sample and hold function.
Note 2: Without sample and hold function, set the
φ
AD
frequency to 250kHz min.
With the sample and hold function, set the
φ
AD
frequency to 1MHz min.
Note 3: Only mask ROM version.
V
CC
= 3V
Resolution
Absolute precision
Operating modes
Analog input pins
A-D Converter
The A-D converter consists of one 10-bit successive approximation A-D converter circuit with a capacitive
coupling amplifier. Pins P10
0
to P10
7
also function as the analog signal input pins. The direction registers of
these pins for A-D conversion must therefore be set to input. The Vref connect bit (bit 5 at address 03D7
16
)
can be used to isolate the resistance ladder of the A-D converter from the reference voltage input pin (V
REF
)
when the A-D converter is not used. Doing so stops any current flowing into the resistance ladder from
V
REF
, reducing the power dissipation. When using the A-D converter, start A-D conversion only after setting
bit 5 of 03D7
16
to connect V
REF
.
The result of A-D conversion is stored in the A-D registers of the selected pins. When set to 10-bit precision,
the low 8 bits are stored in the even addresses and the high 2 bits in the odd addresses. When set to 8-bit
precision, the low 8 bits are stored in the even addresses.
Table 30 shows the performance of the A-D converter. Figure 101 shows the block diagram of the A-D
converter, and Figures 102 and 103 show the A-D converter-related registers.
Table 30. Performance of A-D converter