9. Clock Generation Circuit
9.2.6
Main Clock Oscillator Control Register (MOSCCR)
MOSCCR controls the main clock oscillator.
MOSTP Bit (Main Clock Oscillator Stop)
This bit runs or stops the main clock oscillator.
The main clock oscillator is operated or stopped by the MOSTP bit and main clock oscillator forced oscillation bit in the
main clock oscillator forced oscillation control register (MOFCR.MOFXIN). The main clock oscillator can be started by
setting the MOSTP bit to operating or by setting the MOFXIN bit to forced oscillation. When the MOFXIN bit is set to
forced oscillation, the oscillator operates even in deep software standby mode.
When changing the value of the MOSTP bit or MOFCR.MOFXIN bit, execute subsequent instructions after reading the
When a crystal oscillator is connected to supply the main clock signal, after changing the MOSTP bit or
MOFCR.MOFXIN bit so that the main clock oscillator operates, only use the main clock after the main clock oscillation
stabilization waiting time (crystal; tMAINOSCWT) has elapsed.
When an external clock is connected to supply the main clock signal, after changing the MOSTP bit or
MOFCR.MOFXIN bit so that the main clock oscillator operates, only use the main clock after the EXTAL external clock
input waiting time (tEXWT) has elapsed.
For the main clock oscillator, a fixed time is required for oscillation to become stable after the settings for operation have
been made. Furthermore, a fixed time is required for oscillation to actually stop after the settings to stop oscillation have
been made. Accordingly, take note of the following limitations when starting and stopping PLL operation.
When restarting the main clock after it has been stopped, allow at least five cycles of the main clock as an interval
over which it is still stopped.
Ensure that oscillation by the main clock oscillator is stable when making the setting to stop the main clock
oscillator.
Regardless of whether or not it is selected as the system clock, ensure that oscillation by the main clock oscillator is
stable before executing a WAIT instruction to place the chip on software standby or deep software standby.
When a transition to software standby or deep software standby is to follow the setting to stop the main clock
oscillator, wait for at least two cycles of the main clock before executing the WAIT instruction.
Writing of 1 to the MOSTP bit (stopping the main clock oscillator) is prohibited while the main clock oscillator or PLL is
selected by the clock source select bits in system clock control register 3 (SCKCR3.CKSEL[2:0]).
Address(es): 0008 0032h
b7
b6
b5
b4
b3
b2
b1
b0
——————
—
MOSTP
Value after reset:
00000
001
Bit
Symbol
Bit Name
Description
R/W
b0
Main Clock Oscillator Stop
0: Main clock oscillator is operating.
1: Main clock oscillator is stopped.
R/W
b7 to b1
—
Reserved
These bits are read as 0. The write value should be 0.
R/W