M16C65 Datasheet, PDF (783/829 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/60

Under development
M16C/65 Group
Preliminary Specification
This is a preliminary specification and is subject to change.
31. Precautions
31.6.2 Noise Countermeasure
31.6.2.1 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 oscillator, and (b) the MCU's VSS pin,
with the shortest possible wiring (maximum 20 mm).
Noise
XIN
VSS
XOUT
XIN
VSS
XOUT
Bad
Figure 31.4 Clock I/O Pin Wiring
Good
Reason
If 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 oscillator, an accurate clock is not input to the
MCU.
31.6.2.2 Large Current Signal Line
For large currents that go above the MCU's current range, wire the signal lines as far away from the
MCU as possible (especially the oscillator).
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.
Mutual inductance
M
Large current
GND
Figure 31.5 Large Current Signal Line Wiring
REJ09B0484-0030 Rev.0.30 Sep 09, 2008
Page 748 of 791
MCU
XIN
VSS
XOUT