Datasheet

RL78/L12 CHAPTER 5 CLOCK GENERATOR
R01UH0330EJ0200 Rev.2.00 131
Dec 13, 2013
An external main system clock (fEX = 1 to 20 MHz) can also be supplied from the EXCLK/X2/P122 pin. An external
main system clock input can be disabled by executing the STOP instruction or setting of the MSTOP bit.
As the main system clock, a high-speed system clock (X1 clock or external main system clock) or high-speed on-
chip oscillator clock can be selected by setting of the MCM0 bit (bit 4 of the system clock control register (CKC)).
(2) Subsystem clock
• XT1 clock oscillator
This circuit oscillates a clock of f
XT = 32.768 kHz by connecting a 32.768 kHz resonator to XT1 and XT2.
Oscillation can be stopped by setting the XTSTOP bit (bit 6 of the clock operation status control register (CSC)).
An external subsystem clock (f
EXS = 32.768 KHz) can also be supplied from the EXCLKS/XT2/P124 pin. An
external subsystem clock input can be disabled by setting the XTSTOP bit.
(3) Low-speed on-chip oscillator clock
This circuit oscillates a clock of f
IL = 15 kHz (TYP.).
The low-speed on-chip oscillator clock cannot be used as the CPU clock.
Only the following peripheral hardware runs on the low-speed on-chip oscillator clock.
• Watchdog timer
• Real-time clock
• 12-bit interval timer
• LCD driver/controller
This clock operates when bit 4 (WDTON) of the option byte (000C0H), bit 4 (WUTMMCK0) of the subsystem
clock supply mode control register, or both are set to 1.
However, when WDTON = 1, WUTMMCK0 = 0, and bit 0 (WDSTBYON) of the option byte (000C0H) is 0,
oscillation of the low-speed on-chip oscillator stops if the HALT or STOP instruction is executed.
Caution The low-speed on-chip oscillator clock (f
IL) can only be selected as the real-time clock
operation clock when the fixed-cycle interrupt function is used.
Remark f
X: X1 clock oscillation frequency
f
IH: High-speed on-chip oscillator clock frequency
f
EX: External main system clock frequency
fXT: XT1 clock oscillation frequency
f
EXS: External subsystem clock frequency
f
IL: Low-speed on-chip oscillator clock frequency
<R>