7480 datasheet(253/337 Pages) RENESAS

253 / 337 page

7480 Group and 7481 Group User's Manual

2-38

2.8 Countermeasures against Noise

APPLICATIONS

2.8 Countermeasures against Noise

Countermeasures against noise are described below. The following countermeasures are effective against

noise in theory, however, it is necessary not only to take measures as follows but to evaluate before actual

use.

2.8.1 Shortest Wiring Length

The wiring on a printed circuit board can be as an antenna which feeds noise into the microcomputer.

The shorter the total wiring length (by mm unit), the less the possibility of noise insertion into a microcomputer.

(1)

Wiring for RESET Pin

Make the length of wiring which is connected to the RESET pin as short as possible. Especially,

connect a capacitor across the RESET pin and the VSS pin with the shortest possible wiring (within

20mm).

REASON

The reset works to initialize a microcomputer.

The width of a pulse input into the RESET pin is determined by the timing necessary conditions. If

noise having a shorter pulse width than the standard is input to the RESET pin, the microcomputer

is released from reset before the internal state of the microcomputer is completely initialized. This

may cause a program runaway.

Figure 2.8.1 Wiring for RESET Pin

RESET

Reset

circuit

Noise

VSS

Reset

circuit

VSS

RESET

VSS

7480 Group

7481 Group

7480 Group

7481 Group

N.G.

O.K.

7480 Datasheet(PDF) 253 Page - Renesas Technology Corp