C-Pin; Clock Source - Cypress FR81S CY91F52 Series Recommendation For Hardware Setup

2.8

C-Pin

A 4.7 µF ceramic capacitor (dielectric X7R) must be connected very close to the C pin of the MCU. Furthermore, an
additional 100 nF (dielectric X7R) for higher noise frequencies is recommended. Otherwise the MCU may not operate
correct or will be damaged in worst case. Please refer to Datasheet chapter "Recommended operating conditions" for
further information.
MCU
Vcc
5V
Vss
2.9

Clock Source

A clock source must be provided to the MCU. Therefore, crystals or external clock signals can be used. For external
source pin X0 (X0A) is used whereby pin X1 (X1A) is not connected.
There are MCU derivatives for dual clock and single clock devices, the sub clock can be enabled by software. If sub
clock X0A pin is neither used as GPIO nor as clock input, the pin can be left open.
If you want to use only CR clock, then you need a MCU version with disabled CSV.
Please also refer to the chapter "Handling the device" in the corresponding hardware manual for details.
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Figure 3. Internal Voltage Regulator and C Pin
5V
GND
Vcc Vss
GPIO GPIO GPIO
CORE
Internal 1.2V
internal
voltage
regulator
GPIO GPIO GPIO
Vcc Vss
GND
5V
Document No. 002-09375 Rev. *B
Recommendation for Hardware Setup 32-Bit FR81S Family
Vcc
5V
Vss
C
4.7µF
(ceramic X7R)
Vss
*1
Note *1 : Vss pin
GND
closest to C pin
5