M37274EFSP datasheet(34/148 Pages) RENESAS

34 / 148 page

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER

and ON-SCREEN DISPLAY CONTROLLER

M37274EFSP

PRELIMINARY

Notice:

This

is not

a final

specification.

Some

paramentic

limits

are

subject

to change.

MITSUBISHI MICROCOMPUTERS

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

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,” accordingly providing 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. 27. A-D Comparator Block Diagram

A-D control register

(

address 00EF16)

A-D control circuit

Data bus

Switch tree

A-D conversion

interrupt request

Resistor ladder

Compa-

rator

A-D conversion register

AD1

AD2

AD3

AD4

( address 00EE16 )

VSS VCC

AD5

AD6

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