R01UH0092EJ0110 Rev.1.10
Page 765 of 807
Jul 31, 2012
M16C/64C Group
32. Usage Notes
32.5.2
Noise Countermeasure
32.5.2.1
Clock I/O Pin Wiring
•
Connect the shortest possible wiring to the clock I/O pin.
•
Connect (a) the capacitor's ground lead connected to the crystal/ceramic resonator, and (b) the
MCU's VSS pin, with the shortest possible wiring (maximum 20 mm).
Figure 32.5
Clock I/O Pin Wiring
Reason:
When noise enters the clock I/O pin, the clock waveform becomes unstable, which causes an error in
operation or a program runaway. Also, if a potential difference attributed to the noise occurs between
the VSS level of the MCU and the VSS level of the crystal/ceramic resonator, an accurate clock is not
input to the MCU.
32.5.2.2
Large Current Signal Line
For large currents that exceed the MCU's current range, wire the signal lines as far away from the
MCU as possible (especially the crystal/ceramic resonator).
Reason:
In the system using the MCU, there are signal lines for controlling motors, LEDs, and thermal heads.
When a large current flows through these signal lines, noise is generated due to mutual inductance.
Figure 32.6
Large Current Signal Line Wiring
Bad
XIN
VSS
XOUT
XIN
VSS
XOUT
Good
Noise
XIN
VSS
XOUT
M
Mutual inductance
Large current
MCU
GND
Содержание M16C Series
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