Renesas rl78 User Manual
RL78/G1A
CHAPTER 5 CLOCK GENERATOR
R01UH0305EJ0200 Rev.2.00
140
Jul 04, 2013
(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 the setting of the XTSTOP bit.
(3) Low-speed on-chip oscillator clock (Low-speed on-chip oscillator)
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
This clock operates when bit 4 (WDTON) of the option byte (000C0H), bit 4 (WUTMMCK0) of the subsystem
clock supply mode control register (OSMC), 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 count
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
f
XT
:
XT1 clock oscillation frequency
f
EXS
: External subsystem clock frequency
f
IL
:
Low-speed on-chip oscillator clock frequency
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