7477 datasheet(155/361 Pages) RENESAS

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7470/7471/7477/7478 GROUP USER’S MANUAL

1-148

HARDWARE

1.14 A-D converter

Fig. 1.14.5 Structure of A-D control register

Each bit of the A-D control register is described below.

2 Analog input pin selection bit (Bit 2 to 0)

These bits select an analog input pin.

Pins that are not used as analog input pins of P2 function as programmable I/O ports (input ports

in the 7477/7478 group).

2 A-D conversion end bit (Bit 3)

This bit indicates the operation state of the A-D converter.

This bit is cleared to “0” during A-D conversion and set to “1” upon termination of A-D conversion.

A-D conversion is started by clearing this bit to “0.” (At the time when the bit is cleared to “0” during

A-D conversion, A-D conversion is restarted.)

2 VREF connect selection bit (Bit 4) (The 7477/7478 group is not provided with this bit.)

This bit connects the VREF pin to a ladder resistor.

When using the A-D converter, be sure to set this bit to “1.”

When the A-D converter is not used, power consumption can be reduced by clearing this bit to “0.”

b7 b6 b5 b4 b3 b2 b1 b0

A-D control register (ADCON) [Address

At reset

R W

A-D control register

5, 6

00 0

Name

Function

A-D input selection

bits

0 0 0 : P20/IN0

0 : Under conversion

1 : End conversion

b2 b1 b0

(Note 1)

A-D conversion end

bit

(Note 2)

VREF connection

selection bit

VThe 7477/7478 group is not

provided with this bit.

This bit is undefined at

reset.

Nothing is allocated for these bits.

These are write disabled bits and are

undefined at reading.

Fix this bit to “0.”

?? !

0 0 1 : P21/IN1

0 1 0 : P22/IN2

0 1 1 : P23/IN3

1 0 0 : P24/IN4

1 0 1 : P25/IN5

1 1 0 : P26/IN6

1 1 1 : P27/IN7

0 : The VREF pin is

separated from the

comparison voltage

generator.

1 : The VREF pin is

connected to

comparison voltage

generator.

Notes 1:

Since the 7470/7477 group is not provided with pins

P24–P27, do not set.

•A-D conversion is started by setting bit 3 to “0.”

•Writing “0” into bit 3 is valid. Even if “1” is written into

bit 3, this bit is not set to “1.” Accordingly, when writing a

value into the A-D control register without affecting bit 3,

set bit 3 to “1.”

00D916]

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