3819_03 Datasheet, PDF (189/218 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

3. APPENDIX
MITSUBISHI MICROCOMPUTER
3819 Group
3.2 Countermeasures against noise
Noise
XIN
XOUT
VSS
XIN
XOUT
VSS
An example of VSS patterns on the
underside of a printed circuit board
Oscillator wiring
pattern example
XIN
XOUT
VSS
Separate the VSS line for oscillation from other VSS lines
Fig. 3.2.2 Wiring for clock I/O pins
(3) Wiring for the VPP pin of the One Time PROM
version and the eprom version
qMake the length of wiring which is connected to the
VPP pin as short as possible.
qConnect an approximately 5 kΩ resistor to the VPP
pin in serial.
Reason
The VPP pin of the One Time PROM and the EPROM
version is the power source input pin for the built-in
PROM. When programming in the built-in PROM, the
impedance of the VPP pin is low to allow the electric
current for wiring flow into the PROM. Because of this,
noise can enter easily. If noise enters the VPP pin,
abnormal in struction codes or data are read from the
built-in PROM, which may cause a program runaway.
3819 group
Approximately
5kΩ
P40/VPP
Fig. 3.2.3 Wiring for the VPP pin of the One Time PROM
and the EPROM version
3.2.2 Connection of a bypass capacitor across the
Vss line and the Vcc line
Connect an approximately 0.1 µF bypass capacitor
across the VSS line and the VCC line as follows:
qConnect a bypass capacitor across the VSS pin and
the VCC pin at equal length .
qConnect a bypass capacitor across the VSS pin and
the VCC pin with the shortest possible wiring.
qUse lines with a larger diameter than other signal
lines for VSS line and VCC line.
VCC VSS
Fig. 3.2.4 Bypass capacitor across the VSS line and
the VCC line
3819 Group USER’S MANUAL
175