7477 datasheet(241/354 Pages) RENESAS

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

2-6

APPLICATION

2.1 I/O pins

7470

7471

7477

7478

(2)Description of Pull-up control

When pulling up a port by software, take the following points into consideration.

q When P1 is used in the serial I/O mode, the pull-up settings corresponding to P14 to P17 are

invalidated. (Pull-up is impossible.)

q Pull-up control is exerted in the following bit units.

: 1-bit unit

P1 to P5

: 4-bit unit

When using an external pull-up resistor and software pull-up control for the same port in combined

form, use P0, which can be controlled in bit units.

(3)Notes on external circuit design for I/O ports

1 When designing an external circuit for I/O ports, be sure to set the following items within the

standard value range.

q Sum output current

q Peak output current

q Average output current

Figure 2.1.2 shows the example of external circuit design for I/O port.

Fig. 2.1.2 Example of external circuit design for I/O port

2 When performing multiple key-in operations by forming a key matrix, design in consideration of

the port input current for multiple key-in operations.

2 For other notes, refer to “1.10 I/O Pins.”

M3747x

P00

R0=250

Ω

IOL0=12 mA

P02

P01

R1=250

Ω

R2=250

Ω

IOL2=12 mA

IOL1=12 mA

10 ms

VCC=5 V

“L” average output current (within 100 ms)

12 mA!10 ms!5

“L” sum output current

IOL0

+IOL1+IOL2=36 mA

“L” peak output current

IOL0

=IOL1=IOL2=12 mA

= 6 mA <

100 ms

Maximum standard value

60 mA

20 mA

10 mA

V: LED (VF= 2 V) used

Ports P00 – P02

Timing of LED on

(duty ratio: 50 %)

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