R01UH0823EJ0100 Rev.1.00
Page 200 of 1823
Jul 31, 2019
RX23W Group
9. Clock Generation Circuit
9.5
Dedicated Clock Oscillator for Bluetooth
Operating Bluetooth requires connection to the 32-MHz clock oscillator.
9.5.1
Connecting the Oscillator
An example of connection of the oscillator is shown in
Insert a damping resistor (Rd) as required. Set the resistance to the value recommended by the oscillator manufacturer as
the value depends on the oscillator and its driving capability. If the oscillator manufacturer states that the addition of a
feedback resistor (Rf) to the oscillator is required, insert Rf between XTAL1_RF and XTAL2_RF according to the
instructions.
To control the oscillator, use the Bluetooth middleware provided by Renesas. The Bluetooth middleware is also able to
control the settings of the on-chip variable capacitors, CL1 and CL2, to adjust the frequency of oscillation. Adjustment of
the frequency of the Bluetooth-dedicated clock oscillator is explained in the application note Procedure for Adjusting the
Frequency of the Bluetooth-Dedicated Clock Oscillator (R01AN4762). Obtain the latest version of this document from
the Renesas website.
Figure 9.10
Example of the Connection of a 32-MHz Crystal Resonator
9.5.2
Connecting the Bluetooth-Dedicated Clock Output Pin
When the Bluetooth middleware sets up the clock output and the BLE shifts from waiting mode to RF power-down
mode, the frequency-divided clock for the Bluetooth-dedicated clock is output. If the BLE subsequently shifts to RF low-
power mode, the RF clock output is disabled. The Bluetooth middleware is able to specify the frequency-divisor for the
Bluetooth-dedicated clock.
The Bluetooth-dedicated clock output can also be used as the input of the external clock for the main clock oscillator by
externally connecting the CLKOUT_RF and EXTAL pins on the board. Figure 9.11 shows an example of a configuration
where the Bluetooth-dedicated clock output is used as the input of the external clock for the main clock oscillator.
Figure 9.11
Example of Connection of the Bluetooth-dedicated clock output pin
CL1
XTAL1_RF
Specified from Bluetooth
middleware
On-chip variable capacitor
setting register
XTAL1_RF
CL2
Rf
Rd
XTAL2_RF
Specified from Bluetooth
middleware
EXTAL
XTAL1_RF
Dedicated clock
oscillator for
Bluetooth
Frequency
divider
1/8
1/16
1/32
P47/CLKOUT_RF
32MHz