參數(shù)資料
型號(hào)： M34559G6
廠商： Renesas Technology Corp.
英文描述： SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER
中文描述： 單芯片4位微機(jī)的CMOS
文件頁數(shù)： 72/148頁
文件大?。?/td> 1732K
代理商： M34559G6
Rev.1.04
REJ03B0188-0104
Aug 23, 2007
Page 72 of 146
4559 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
follows but to evaluate before actual use.
(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 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 V
SS
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 microcomputer is completely initialized.
This may cause a program runaway.
Fig 74. 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 across the grounding lead of a
capacitor which is connected to an oscillator and the V
SS
pin of a microcomputer as short as possible.
Separate the V
SS
pattern only for oscillation from other
V
SS
patterns.
Fig 75. Wiring for clock I/O pins
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 V
SS
level of a microcomputer and the V
SS
level of an
oscillator, the correct clock will not be input in the
microcomputer.
(3) Wiring to CNV
SS
pin
Connect an approximately 5 k
resistor to the V
PP
pin and
also to the GND pattern supplied to the V
SS
pin with
shortest possible wiring.
Reason
The CNV
SS
pin is the power source input pin for the built-in
QzROM. When programming in the built-in QzROM, the
impedance of the CNV
SS
pin is low to allow the electric
current for writing flow into the QzROM. Because of this,
noise can enter easily. If noise enters the CNV
SS
pin, abnormal
instruction codes or data are read from the built-in QzROM,
which may cause a program runaway.
Fig 76. Wiring for CNV
SS
pin
RESET
Reset
circuit
Noise
V
SS
V
SS
N.G.
Reset
circuit
V
SS
RESET
V
SS
O.K.
Noise
X
IN
X
OUT
V
SS
N.G.
X
IN
X
OUT
V
SS
O.K.
CNVss
V
SS
The shortest
The shortest
about 5k
Note: This indicates pin.
(Note)
(Note)
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