7477 datasheet(161/354 Pages) RENESAS

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

1-144

HARDWARE

1.14 A-D converter

1.14.2 Pins

The pins used in the A-D converter are described below.

(1) Analog input pin (P20/IN0 to P27/IN7) (P20/IN0 to P23/IN3 in the 7470/7477 group)

q The analog input pin is an input pin for analog voltage.

q Apply a voltage of VSS (AVSS) - VREF to this pin.

q This pin is used in common with P20 to P27 (P20 to P23 in the 7470/7477 group).

When using the A-D converter, select a pin to be used as an analog input pin by bit 2 to bit 0 of

the A-D control register (ADCON: address 00D916).

Use the A-D converter in the following condition in the 7470/7471 group.

• When the bit of the Port P2 direction register, which corresponds to the used analog input pin,

is “0” (input mode)

• When the bit of the Pull-up control register, which corresponds to the used analog input pin, is

“0” (no pull-up)

(2) Reference voltage input pin (VREF)

q The reference voltage input pin is an input pin for reference voltage.

q Input a voltage of 0.5 VCC (

>2) - VCC [V].

(3) Analog power source input pin (AVSS)

q Analog power source input pin is an input pin for GND.

q Apply the same potential as the VSS pin to this pin.

q This pin is dedicated to the 56P6N-A package product of the 7471/7478 group.

1.14.3 Notes on use

When using the A-D converter, take the following points into consideration.

2 The comparator is configured by capacity coupling, so the charge is lost if the clock input oscillation

frequency is low.

q Set f(XIN) at 1 MHz or more during A-D conversion.

q Don’t execute the STP instruction during A-D conversion.

2 Apply a voltage of 0.5 VCC (>2) - VCC [V] to the reference voltage input pin VREF.

Note that if the reference voltage is lowered below the above valve, the A-D conversion precision will

be degraded.

2 Apply the same potential as that of the VSS pin to the analog power supply voltage input pin AVSS.

The AVSS pin is dedicated to the 56P6N-A package product of the 7471/7478 group.

2 In the 7470/7471 group, clear the bit of the Port P2 direction register which corresponds to the used

analog input pin to “0” (input mode).

2 In the 7470/7471 group, clear the bit of the Pull-up control register which corresponds to the used

analog input pin to “0” (no pull-up).

7477 Datasheet(PDF) 161 Page - Renesas Technology Corp