3822 datasheet(74/328 Pages) RENESAS

74 / 328 page

APPLICATION

2.1 I/O pins

3822 GROUP USER’S MANUAL

2–8

2.1.3 Application examples

The basic structure for key input without a pull-up resistor and an application examples of it are described

below.

In contrast to a method which uses a pull-up resistor, dissipating current incessantly, this method requires

only a charging current for a very small capacitance, so it is especially suitable for a battery-driven unit.

In the following description, ports A, B, C and D are only tentative names and differ from the real port

names.

(1) Basic structure for key input

Fig. 2.1.7 Connection example 1 for key input

Figure 2.1.7 shows a connection example 1 for

key input without a pull-up resistor and Figure

2.1.8 shows the key input control procedure 1.

Figure 2.1.9 shows a timing diagram 1 where

switch A is pressed.

Fig. 2.1.8 Key input control procedure 1

CMOS I/O

port A

CMOS I/O

port B

CMOS I/O

port C

SW A

SW B

SW C

r = 10 k

Ω

Virtual

capacitor (C)

Key input

Output “H” for charging to each

port

V1 In the case of no key input, output “L” (Noise counter-

measure).

V2 A virtual capacitor (C) is charged by outputting “H.”

(For capacitance, refer to the next page.)

V3 Set the port direction register for input mode with an

instruction immediately after “H” is output.

(For the limit timer for ON/OFF judgment and the

discharging time at ON, refer to the next page.)

V4 For double reading to ensure data, repeat V2 and V3.

After inputting data into the port

direction register, judge ON/OFF

of key input.

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