RL78/D1A User's Manual: Hardware - Renesas

Under development
Preliminary document
Specifications in this document are tentative and subject to change.
RL78/D1A CHAPTER 5 CLOCK GENERATOR
5.5 System Clock Oscillator
5.5.1 X1 oscillator
The X1 oscillator oscillates with a crystal resonator or ceramic resonator (1 to 20 MHz) connected to the X1 and X2
pins.
An external clock can also be input. In this case, input the clock signal to the EXCLK pin.
To use the X1 oscillator, set bits 7 and 6 (EXCLK, OSCSEL) of the clock operation mode control register (CMC) as
follows.
Crystal or ceramic oscillation: EXCLK, OSCSEL = 0, 1
External clock input: EXCLK, OSCSEL = 1, 1
When the X1 oscillator is not used, set the input port mode (EXCLK, OSCSEL = 0, 0).
When the pins are not used as input port pins, either, see Chapter 2.3 Pin I/O Circuits and Recommended
Connection of Unused Pins.
Figure 5-16 shows an example of the external circuit of the X1 oscillator.
Figure 5-16. Example of External Circuit of X1 Oscillator
(a) Crystal or ceramic oscillation (b) External clock
Crystal resonator
or
ceramic resonator
VSS
X1
X2
Cautions are listed on the next page.
External clock
EXCLK
5.5.2 XT1 oscillator
The XT1 oscillator oscillates with a crystal resonator (standard: 32.768 kHz) connected to the XT1 and XT2 pins.
To use the XT1 oscillator, set bit 4 (OSCSELS) of the clock operation mode control register (CMC) to 1.
Crystal or ceramic oscillation: OSCSELS = 1
When the XT1 oscillator is not used, set the input port mode (OSCSELS = 0).
When the pins are not used as input port pins, either, see Chapter 2.3 Pin I/O Circuits and Recommended
Connection of Unused Pins.
Figure 5-17 shows an example of the external circuit of the XT1 oscillator.
R01UH0317EJ0004 Rev. 0.04 291
Feb. 22, 2013