4552 Datasheet, PDF (61/145 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4552 Group
(3) Wiring to CNVSS pin
Connect CNVSS pin to a GND pattern at the shortest distance.
The GND pattern is required to be as close as possible to the GND
supplied to VSS.
In order to improve the noise reduction, to connect a 5 kΩ resistor
serially to the CNVSS pin - GND line may be valid.
As well as the above-mentioned, in this case, connect to a GND
pattern at the shortest distance. The GND pattern is required to be
as close as possible to the GND supplied to VSS.
<Reason>
The CNVSS pin of the One Time PROM is the power source input
pin for the built-in One Time PROM. When programming in the
built-in One Time PROM, the impedance of the CNVSS pin is low to
allow the electric current for writing flow into the One Time PROM.
Because of this, noise can enter easily. If noise enters the CNVSS
pin, abnormal instruction codes or data are read from the built-in
One Time PROM, which may cause a program runaway.
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
(Note) The shortest
CNVSS
VSS
(Note)
About 5kΩ
The shortest
Note: This indicates pin.
Fig. 56 Wiring for the CNVSS pin of the One Time PROM
VSS
VSS
N.G.
O.K.
Fig. 57 Bypass capacitor across the VSS line and the VDD line
Rev.3.02 Dec 22, 2006 page 61 of 142
REJ03B0023-0302