M38258MCM Datasheet, PDF (29/70 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS
3825 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 (AD)] 003516
The A-D conversion register is a read-only register that contains
the result of an A-D conversion. When reading this register during
an A-D conversion, the previous conversion result is read.
[A-D Control Register (ADCON)] 003416
The A-D control register controls the A-D conversion process. Bits
0 to 2 of this register select specific analog input pins. Bit 3 signals
the completion of an A-D conversion. The value of this bit remains
at “0” during an A-D conversion, then changes to “1” when the A-
D conversion is completed. Writing “0” to this bit starts the A-D
conversion. Bit 4 controls the transistor which breaks the through
current of the resistor ladder. When bit 5, which is the AD external
trigger valid bit, is set to “1”, this bit enables A-D conversion even
by a falling edge of an ADT input. Set ports which share with ADT
pins to input when using an A-D external trigger.
Comparison Voltage Generator
The comparison voltage generator divides the voltage between
AVSS and VREF by 256, and outputs the divided voltages.
Channel Selector
The channel selector selects one of the input ports P67/AN7–P60/
AN0.
Comparator and Control Circuit
The comparator and control circuit compare an analog input volt-
age with the comparison voltage and store the result in the A-D
conversion register. When an A-D conversion is completed, 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 at least 500kHz during A-D conversion.
Use the clock divided from the main clock XIN as the internal clock
φ.
b7
b0
A-D control register
(ADCON : address 003416)
Analog input pin selection bits
0 0 0 : P60/AN0
0 0 1 : P61/AN1
0 1 0 : P62/AN2
0 1 1 : P63/AN3
1 0 0 : P64/AN4
1 0 1 : P65/AN5
1 1 0 : P66/AN6
1 1 1 : P67/AN7
AD conversion completion bit
0 : Conversion in progress
1 : Conversion completed
VREF input switch bit
0 : OFF
1 : ON
AD external trigger valid bit
0 : A-D external trigger invalid
1 : A-D external trigger valid
Interrupt source selection bit
0 : Interrupt request at A-D
conversion completed
1 : Interrupt request at ADT
input falling
Not used (returns “0” when read)
Fig. 26 Structure of A-D control register
Data bus
b7
b0
A-D control register
P57/ADT
3
P60/AN0
P61/AN1
P62/AN2
P63/AN3
P64/AN4
P65/AN5
P66/AN6
P67/AN7
A-D control circuit
Comparator
A-D conversion
register
8
Resistor ladder
AVSS VREF
Fig. 27 A-D converter block diagram
ADT/A-D interrupt request
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