7477 datasheet(288/354 Pages) RENESAS

Part #	7477

Description	8-BIT SINGLE-CHIP MICROCOMPUTER 740 FAMILY / 7470 SERIES

PDF	354 Pages

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Manufacturer	RENESAS [Renesas Technology Corp]

Direct Link	http://www.renesas.com

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288 / 354 page

2-53

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

APPLICATION

2.9 Countermeasures against noise

7470

7471

7477

7478

2.9.5 Setup for I/O ports

Setup I/O ports using hardware and software as follows:

q Connect a resistor of 100

Ω or more to an I/O port

inseries.

q As for an input port, read data several times by a

program for checking whether input levels are equal

or not.

q As for an output port, since the output data may

reverse because of noise, rewrite data to its port

latch at fixed periods.

q Rewrite data to direction registers and pull-up control

registers (only the product having it) at fixed periods.

When a direction register is set for input port again

at fixed periods, a several-nanosecond short pulse

may be output from this port. If this is undesirable,

connect a capacitor to this port to remove the

noise pulse.

Fig. 2.9.8 Setup for I/O ports

,,,,

Direction register

Port latch

Data bus

I/O port

pins

Noise

O.K.

N.G.

7477 Datasheet(PDF) 288 Page - Renesas Technology Corp