Technical information

25
MITSUBISHI MICROCOMPUTERS
3806 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
A-D Converter
The functional blocks of the A-D converter are described below.
[A-D conversion register]
The A-D conversion register is a read-only register that stores the
result of an A-D conversion. When reading this register during an
A-D conversion, the previous conversion result is read.
[AD/DA control register]
The AD/DA control register controls the A-D conversion process.
Bits 0 to 2 select a specific analog input pin. Bit 3 signals 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.
Bits 6 and 7 are used to control the output of the D-A converter.
[Comparison voltage generator]
The comparison voltage generator divides the voltage between
AVSS and VREF into 256, and outputs the divided voltages.
[Channel selector]
The channel selector selects one of the ports P60/AN0 to P67/AN7,
and inputs the voltage to the comparator.
Fig.18 Structure of AD/DA control register
Fig. 19 Block diagram of A-D converter
[Comparator and Control circuit]
The comparator and control circuit compares an analog input volt-
age with the comparison voltage, then stores the result in the A-D
conversion register. When an A-D conversion is complete, the
control circuit sets the AD conversion completion bit and the AD
interrupt request bit to “1”.
Note that the comparator is constructed linked to a capacitor, so
set f(XIN) to 500 kHz or more during an A-D conversion.
AD/DA control register
(ADCON : address 0034
16 )
Analog input pin selection bits
0 0 0: P6
0 /AN 0
0 0 1: P6 1 /AN 1
0 1 0: P6 2 /AN 2
0 1 1: P6 3 /AN 3
1 0 0: P6 4 /AN 4
1 0 1: P6 5 /AN 5
1 1 0: P6 6 /AN 6
1 1 1: P6 7 /AN 7
AD conversion completion bit
0: Conversion in progress
1: Conversion completed
Not used (return "0" When read)
DA
1 output enable bit
0: DA
1 output disabled
1: DA
1 output enabled
DA
2 output enable bit
0: DA
2 output disabled
1: DA
2 output enabled
b7
b0
b2 b1 b0
Channel selector
A-D control circuit
A-D conversion register
Resistor ladder
V
REF AVSS
Comparator
A-D interrupt request
b7 b0
3
8
P60/AN0
P61/AN1
P62/AN2
P63/AN3
P64/AN4
P65/AN5
P66/AN6
P67/AN7
Data bus
(Address 0035
16)
AD/DA control register
(Address 0034
16)