33
3851 Group
(Built-in 16 KB ROM)
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
A-D CONVERTER
[A-D Conversion Registers (ADL, ADH)]
0035
16, 003616
The A-D conversion registers are read-only registers that store the
result of an A-D conversion. Do not read these registers during an
A-D conversion
[AD Control Register (ADCON)] 003416
The AD control register controls the A-D conversion process. Bits
0 to 2 select a specific analog input pin. Bit 4 indicates the
completion of an A-D conversion. The value of this bit remains at
“0” during an A-D conversion and changes to “1” when an A-D
conversion ends. Writing “0” to this bit starts the A-D conversion.
Comparison Voltage Generator
The comparison voltage generator divides the voltage between
AVSS and VREF into 1024 and outputs the divided voltages.
Channel Selector
The channel selector selects one of ports P30/AN0 to P34/AN4 and
inputs the voltage to the comparator.
Comparator and Control Circuit
The comparator and control circuit compare an analog input volt-
age with the comparison voltage, and the result is stored in the
A-D conversion registers. When an A-D conversion is completed,
the control circuit sets the A-D conversion completion bit and the
A-D interrupt request bit to “1”.
Note that because the comparator consists of a capacitor cou-
pling, set f(XIN) to 500 kHz or more during an A-D conversion.
Fig. 36 Structure of AD control register
Fig. 37 Structure of A-D conversion registers
AD control register
(ADCON : address 0034
16
)
Analog input pin selection bits
0 0 0: P3
0
/AN
0
0 0 1: P3
1
/AN
1
0 1 0: P3
2
/AN
2
0 1 1: P3
3
/AN
3
1 0 0: P3
4
/AN
4
Not used (returns “0” when read)
A-D conversion completion bit
0: Conversion in progress
1: Conversion completed
Not used (returns “0” when read)
b7
b0
b2 b1 b0
10-bit reading
(Read address 0036
16
before 0035
16
)
(Address 0036
16
)
(Address 0035
16
)
8-bit reading (Read only address 0035
16
)
(Address 0035
16
)
b8
b7 b6 b5 b4 b3 b2 b1 b0
b7 b0
b9
b7
b0
Note : The high-order 6 bits of address 0036
16 become “0”
at reading.
b9 b8 b7 b6 b5 b4 b3 b2
b7
b0
Channel selector
A-D control circuit
A-D conversion low-order register
Resistor ladder
V
REF
AV
SS
Comparator
A-D interrupt request
b7 b0
3
10
P3
0
/AN
0
P3
1
/AN
1
P3
2
/AN
2
P3
3
/AN
3
P3
4
/AN
4
Data bus
AD control register
A-D conversion high-order register
(Address 0034
16
)
(Address 0036
16
)
(Address 0035
16
)
Fig. 38 Block diagram of A-D converter
(88 Seiten)
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