Renesas M32R/ECU Series User Manual page 830

Appendix 4
(3) Wiring of the VCNT pin
Use as much thick and short wiring as possible for connections to the VCNT pin.
When connecting a capacitor to VCNT, make sure its grounding lead wire and the OSC-VSS pin on the
microcomputer are connected in the shortest distance possible.
Also, make sure the VSS pattern used for VCNT is a large ground plane and is connected to GND.
<Reasons>
The external circuit inserted for the VCNT pin plays the role of a low-pass filter that stabilizes the PLL's
internal voltage and eliminates noise. If noise exceeding the limit of the low-pass filter penetrates into the
wiring, the internal circuit may be disturbed by that noise and become unable to produce a precise clock,
causing the microcomputer to operate erratically or get out of control.
Thin and long wiring
Figure 4.13.3 Example Wiring of the VCNT Pin
(4) Wiring of the operation mode setup pins
When connecting the operation mode setup pins and the VCC or VSS pin, make sure they are wired in the
shortest distance possible.
<Reasons>
The levels of the operation mode setup pins affect the microcomputer's operation mode. When connect-
ing the operation mode setup pins and the VCC or VSS pin, be careful that no noise-induced potential
difference will exist between the operation mode setup pins and the VCC or VSS pin. This is because the
presence of such a potential difference makes operation mode instable, which may result in the micro-
computer operating erratically or getting out of control.
Figure 4.13.4 Example Wiring of the MOD0 and MOD1 Pins
Noise
OSC-VSS
VCNT
VSS
Noise
Operation mode
setup pins
VSS
Long wiring
Appendix 4-25
SUMMARY OF PRECAUTIONS
Appendix 4.13 Precautions about Noise
OSC-VSS
VCNT
VSS
Thick and short wiring
Operation mode
setup pins
VSS
Short wiring
32180 Group User's Manual (Rev. 1.0)