Renesas RA Family
RA2 Quick Design Guide
R01AN6060EU0100 Rev.1.00
Page 16 of 44
Sep.14.21
a reduced component count in a PCB design. However, there are performance tradeoffs and limitations due
to the clock accuracy which should be evaluated for your application.
For RA2E2 devices, there are is no external crystal or external clock input. An internal clock (HOCO, MOCO,
or LOCO) must be selected as the main system clock.
5.7 Flash Interface Clock
On RA2A1 devices, the Flash interface Clock (FCLK) is used as the operating clock when programming and
erasing internal flash (ROM and DF) and for reading from the data flash. For other RA2 devices, ICLK is
used as the operating clock when programming and erasing the internal flash.
Therefore, the frequency setting of the relevant clock will have a direct impact on the amount of time it takes
to read from the data flash. If the user’s program is reading from the data flash, or performing programming
or erasures on internal flash, then using the maximum FCLK or ICLK frequency is recommended.
The flash programming clock must run at a frequency of at least 1 MHz when writing or erasing ROM or data
flash. Please note that the clock frequency does not have any impact upon reading from ROM or reading and
writing to RAM.
5.8
Board Design
Refer to the “Usage Notes” section of the Clock Generation Circuit (CGC) chapter in the Hardware User’s
Manual for more information on using the CGC and for board design recommendations.
In general, place the crystal resonator and its load capacitors as close to the MCU clock pins (XTAL/EXTAL,
XCIN/XCOUT) as possible. Avoid routing any other signals between the crystal resonator and the MCU.
Minimize the number of connecting vias used on each trace.
5.9 External Crystal Resonator selection
An external crystal resonator may be used as the main clock source for most RA2 devices. The external
crystal resonator is connected across the EXTAL and XTAL pins of the MCU. The frequency of the external
crystal resonator must be in the frequency range of the main clock oscillator.
Selection of a crystal resonator will be largely dependent on each unique board design. Due to the large
selection of crystal resonators available that may be suitable for use with RA2 MCU devices, carefully
evaluate the electrical characteristics of the selected crystal resonator to determine the specific
implementation requirements.
The following diagram shows a typical example of a crystal resonator connection.
Figure 10. Example of Crystal Resonator Connection
Careful evaluation must be used when selecting the crystal resonator and the associated capacitors. The
external feedback resistor (R
f
) and damping resistor (R
d
) may be added if recommended by the crystal
resonator manufacturer.
