Datasheet

CHAPTER 5 CLOCK GENERATOR
User’s Manual U18698EJ1V0UD
141
Table 5-8. Maximum Time Required for Main System Clock Switchover
Set Value Before Switchover Set Value After Switchover
MCM0 MCM0
0 1
0 1 + 2fRH/fXH clock
1 1 + 2fXH/fRH clock
Caution When switching the internal high-speed oscillation clock to the high-speed system clock, bit 2
(XSEL) of MCM must be set to 1 in advance. The value of XSEL can be changed only once after a
reset release.
Remarks 1. The number of clocks listed in Table 5-8 is the number of main system clocks before switchover.
2. Calculate the number of clocks in Table 5-8 by removing the decimal portion.
Example When switching the main system clock from the internal high-speed oscillation clock to the
high-speed system clock (@ oscillation with fRH = 8 MHz, fXH = 10 MHz)
1 + 2fRH/fXH = 1 + 2 × 8/10 = 1 + 2 × 0.8 = 1 + 1.6 = 2.6 → 2 clocks
5.6.9 Conditions before clock oscillation is stopped
The following lists the register flag settings for stopping the clock oscillation (disabling external clock input) and
conditions before the clock oscillation is stopped.
Table 5-9. Conditions Before the Clock Oscillation Is Stopped and Flag Settings
Clock
Conditions Before Clock Oscillation Is Stopped
(External Clock Input Disabled)
Flag Settings of SFR
Register
Internal high-speed
oscillation clock
MCS = 1 or CLS = 1
(The CPU is operating on a clock other than the internal high-speed
oscillation clock)
RSTOP = 1
X1 clock
External main system clock
MCS = 0 or CLS = 1
(The CPU is operating on a clock other than the high-speed system clock)
MSTOP = 1
XT1 clock
CLS = 0
(The CPU is operating on a clock other than the subsystem clock)
OSCSELS = 0