4501_M Datasheet, PDF (206/212 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 4500 SERIES

4501 Group
APPENDIX
3.4 Notes on noise
(5) Wiring to VPP pin of built-in PROM version
In the built-in PROM version of the 4501 Group,
the CNVSS pin is also used as the built-in
PROM power supply input pin VPP.
q When the VPP pin is also used as the
CNVSS pin
Connect an approximately 5 kΩ resistor to
the VPP pin the shortest possible in series
and also to the VSS pin. When not
connecting the resistor, make the length of
wiring between the VPP pin and the VSS
pin the shortest possible (refer to Figure
3.4.5)
Note: Even when a circuit which included an
approximately 5 kΩ resistor is used in the
Mask ROM version, the microcomputer
operates correctly.
3.4.2 Connection of bypass capacitor across VSS
line and VDD line
Connect an approximately 0.1 µF bypass capacitor
across the VSS line and the VDD line as follows:
• Connect a bypass capacitor across the VSS pin
and the VDD pin at equal length.
• Connect a bypass capacitor across the VSS pin
and the VDD pin with the shortest possible wiring.
• Use lines with a larger diameter than other signal
lines for VSS line and VDD line.
• Connect the power source wiring via a bypass
capacitor to the VSS pin and the VDD pin.
VDD
VDD
q Reason
The VPP pin of the built-in PROM 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 writing
flow into the PROM. Because of this, noise
can enter easily. If noise enters the VPP
pin, abnormal instruction codes or data are
read from the built-in PROM, which may
cause a program runaway.
VSS
VSS
N.G.
O.K.
Fig. 3.4.6 Bypass capacitor across the VSS line
and the VDD line
When the VPP pin is also used as the CNVSS pin
CNVSS/VPP
Approximately
5kΩ
VSS
In the shortest
distance
Fig. 3.4.5 Wiring for the VPP pin of the built-in
PROM version
Rev.2.01 Feb 07, 2005
REJ09B0192-0201
3-37