r5f21346mnfp Renesas Electronics Corporation., r5f21346mnfp Datasheet - Page 764

• Manufacturer Part Number: r5f21346mnfp
• Description: Single-chip Mcus Incorporates The R8c Cpu Core
• Manufacturer: Renesas Electronics Corporation.

R8C/34M Group
R01UH0131EJ0100 Rev.1.00
Jun 21, 2011
35.18 Notes on Noise
35.19 Note on Supply Voltage Fluctuation
Figure 35.7
35.18.1 Inserting a Bypass Capacitor between VCC and VSS Pins as a Countermeasure
35.18.2 Countermeasures against Noise Error of Port Control Registers
After reset is deasserted, the supply voltage applied to the VCC pin must meet either or both the allowable ripple
voltage Vr (vcc) or ripple voltage falling gradient dVr (vcc)/dt shown in Figure 35.7.
VCC
Vr (vcc)
dVr (vcc)/dt
Connect a bypass capacitor (approximately 0.1 µ F) using the shortest and thickest wire possible.
During rigorous noise testing or the like, external noise (mainly power supply system noise) can exceed the
capacity of the MCU’s internal noise control circuitry. In such cases the contents of the port related registers
may be changed.
As a firmware countermeasure, it is recommended that the port registers, port direction registers, and pull-up
control registers be reset periodically. However, examine the control processing fully before introducing the
reset routine as conflicts may be created between the reset routine and interrupt routines.
Symbol
against Noise and Latch-up
Definition of ripple voltage
Allowable ripple voltage
Ripple voltage falling gradient
Parameter
Min.
Standard
Typ.
0.1 VCC
Max.
10
35. Usage Notes
Page 732 of 740
V/ms
Unit
V
Vr (vcc)