參數(shù)資料
型號: M34556M8H-XXXFP
元件分類: 微控制器/微處理器
英文描述: 4-BIT, MROM, 6 MHz, MICROCONTROLLER, PDSO42
封裝: 0.450 INCH, 0.80 MM PITCH, PLASTIC, SSOP-42
文件頁數(shù): 107/147頁
文件大?。?/td> 1087K
代理商: M34556M8H-XXXFP
Rev.3.02
Dec 22, 2006
page 60 of 142
REJ03B0025-0302
4556 Group
NOTES ON 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 fol-
lows but to evaluate before actual use.
1. Shortest wiring length
(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.
<Reason>
In order to reset a microcomputer correctly, 1 machine cycle or
more of the width of a pulse input into the RESET pin is required.
If noise having a shorter pulse width than this is input to the RESET
input pin, the reset is released before the internal state of the mi-
crocomputer is completely initialized.
This may cause a program runaway.
Fig. 54 Wiring for the RESET 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 across the grounding lead of a capaci-
tor 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 pat-
terns.
<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.
RESET
Reset
circuit
Noise
VSS
Reset
circuit
VSS
RESET
VSS
N.G.
O.K.
Noise
XIN
XOUT
VSS
XIN
XOUT
VSS
N.G.
O.K.
Fig. 55 Wiring for clock I/O pins
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