7630 datasheet(188/238 Pages) RENESAS

188 / 238 page

7630 Group User’s Manual

3-17

APPENDIX

3.4 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.

3.4.1 Shortest wiring length

The wiring on a printed circuit board can function 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 the RESET input pin

____________

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

____________

a capacitor across the RESET input pin and the VSS pin with the shortest possible wiring (within 20mm).

Reason

____________

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 input pin, the reset is released before the internal

state of the microcomputer is completely initialized. This may cause a program runaway.

RESET

Reset

circuit

Noise

VSS

Reset

circuit

VSS

RESET

VSS

7630 group

N.G.

O.K.

____________

Fig. 3.4.1 Wiring for the RESET input pin

(2) Wiring for clock input/output pins

• Make the length of wiring which is connected

to clock I/O pins as short as possible.

• Make the length of wiring (within 20mm) across

the grounding lead of a capacitor which is

connected to an oscillator and the VSS pin of

a microcomputer as short as possible.

• Separate the VSS pattern only for oscillation

from other VSS patterns.

Reason

If noise enters clock I/O pins, clock waveforms

may be deformed. This may cause a program

failure or program runaway. Also, if a potential

difference is caused by the noise between the

VSS level of a microcomputer and the VSS level

of an oscillator, the correct clock will not be input

in the microcomputer.

Fig. 3.4.2 Wiring for clock I/O pins

Noise

XIN

XOUT

VSS

XIN

XOUT

VSS

N.G.

O.K.

7630 Datasheet(PDF) 188 Page - Renesas Technology Corp

7630 Datasheet(HTML) 188 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL