m37905 Renesas Electronics Corporation., m37905 Datasheet - Page 535

• Manufacturer Part Number: m37905
• Description: Mitsubishi 16-bit Single-chip Microcomputer 7700 Family / 7900 Series
• Manufacturer: Renesas Electronics Corporation.

countermeasure depends on each system.
APPENDIX
Appendix 7. Countermeasure against noise
Appendix 7. Countermeasure against noise
General countermeasure examples against noise are described below. Although the effect of these
The user shall modify them according to the actual application and test them.
Fig. 2 Wiring for
20-104
1. Short wiring length
The wiring on a printed circuit board may function as an antenna which feeds noise into the microcomputer.
The shorter the total wiring length (by mm unit), the less possibility of noise insertion into the microcomputer.
(1)
(2) Wiring for clock input/output pins
Wiring for
wiring (within 20 mm).
Reason:
Make the length of wiring connected to the RESET pin as short as possible.
In particular, connect a capacitor between the RESET pin and the Vss pin with the shortest possible
Reason: The microcomputer’s operation
Make the length of wiring connected to the clock input/output pins as short as possible.
Make the length of wiring between the grounding lead of the capacitor, which is connected to
Separate the Vss pattern for oscillation from all other Vss patterns. (See Figure 10.)
the oscillator, and the Vss pin of the microcomputer, as short as possible (within 20 mm).
If noise is input to the RESET pin, the microcomputer restarts operation before the internal
state of the microcomputer is completely initialized. This may cause a program runaway.
synchronizes with a clock generated
by the oscillation circuit.
If noise enters clock I/O pins, clock
waveforms may be deformed. This
may cause a malfunction or a
program runaway.
Also, if the noise causes a potential
difference between the Vss level of
the microcomputer and the Vss level
of an oscillator, the correct clock
w i l l
microcomputer.
Reset
circuit
RESET
RESET
______
______
Vss
Not acceptable
n o t
pin
pin
b e
Noise
i n p u t
7905 Group User’s Manual Rev.1.0
______
Vss
RESET
i n
M37905
t h e
______
______
Fig. 3 Wiring for clock input/output pins
Not acceptable
Acceptable
Noise
Reset
circuit
Vss
Vss
X
X
M37905
IN
OUT
Vss
RESET
M37905
Acceptable
X
X
Vss
M37905
IN
OUT