MITSUBISHI MICROCOMPUTERS
M37271MF-XXXSP
M37271EF-XXXSP, M37271EFSP
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER
and ON-SCREEN DISPLAY CONTROLLER
26
A-D control register
(ADCON: address 00EF
16
)
A-D conversion completion bit
0 : Conversion in purogress
1 : Conversion completed
Analog input pin selection bits
b1 b0
0
0 : P2
6
/AD1
0 1 : P2
5
/AD2
1 0 : P2
4
/AD3
1 1 : P4
0
/AD4
V
CC
connection selection bit
0 : OFF
1 : ON
Fix this bit to “0.”
0
70
A-D CONVERTER
(1)A-D Conversion Register (AD)
A-D conversion reigister is a read-only register that stores the result
of an A-D conversion. This register should not be read during A-D
conversion.
(2)A-D Control Register (ADCON)
The A-D control register controls A-D conversion. Bits 1 and 0 of this
register select analog input pins. When these pins are not used as
anlog input pins, they are used as ordinary I/O pins. Bit 3 is the A-D
conversion completion bit, A-D conversion is started by writing “0” to
this bit. The value of this bit remains at “0” during an A-D conversion,
then changes to “1” when the A-D conversion is completed.
Bit 4 controls connection between the resistor ladder and VCC. When
not using the A-D converter, the resistor ladder can be cut off from
the internal VCC by setting this bit to “0.” This can realize the low-
power dissipation.
(3)Comparison Voltage Generator (Resistor
Ladder)
The voltage generator divides the voltage between VSS and VCC by
256, and outputs the divided voltages to the comparator as the refer-
ence voltage Vref.
(4)Channel Selector
The channel selector connects an analog input pin selected by bits 1
and 0 of the A-D control register to the comparator.
(5)Comparator and Control Circuit
The conversion result of the analog input voltage and the reference
voltage “Vref” is stored in the A-D conversion register. The A-D con-
version completion bit and A-D conversion interrupt request bit are
set to “1” at the completion of A-D conversion.
Fig. 19. A-D comparator block diagram
Fig. 18. Structure of A-D control register
A-D control register
(address 00EF
16
)
A-D control circuit
Data bus
Switch tree
A-D conversion
interrupt request
Resistor ladder
Compa-
rator
Channel selector
A-D conversion register
P2
6
/AD1
P2
5
/AD2
P2
4
/AD3
P4
0
/AD4
(address 00EE
16
)
b7 b0
2
8
V
SS
V
CC
(145 Seiten)
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