參數(shù)資料
型號: M34551E8FP
元件分類: 微控制器/微處理器
英文描述: 4-BIT, OTPROM, 8 MHz, MICROCONTROLLER, PQFP48
封裝: 7 X 10 MM, 0.65 MM PITCH, PLASTIC, QFP-48
文件頁數(shù): 50/155頁
文件大?。?/td> 1329K
代理商: M34551E8FP
4551 Group User’s Manual
APPENDIX
3-13
3.4 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 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)
Package
Select the smallest possible package to make
the total wiring length short.
q Reason
The wiring length depends on a microcom-
puter package. Use of a small package,
for example QFP and not DIP, makes the
total wiring length short to reduce influence
of noise.
Fig. 3.4.1 Selection of packages
(2)
Wiring for 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).
q 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.
DIP
SDIP
SOP
QFP
Fig. 3.4.2 Wiring for the RESET input pin
RESET
Reset
circuit
Noise
VSS
Reset
circuit
VSS
RESET
VSS
N.G.
O.K.
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