
CHAPTER 6 CLOCK GENERATOR
User’s Manual U17260EJ6V0UD
170
Table 6-5. CPU Clock Transition and SFR Register Setting Examples (2/4)
(4) CPU clock changing from internal high-speed oscillation clock (B) to high-speed system clock (C)
(Setting sequence of SFR registers)
Setting Flag of SFR Register
Status Transition
AMPH
Note
EXCLK
OSCSEL
MSTOP
OSTC
Register
XSEL
Note
MCM0
(B)
→ (C) (X1 clock: 1 MHz ≤ fXH ≤ 10 MHz)
0
1
0
Must be
checked
1
(B)
→ (C) (external main clock: 1 MHz ≤ fXH ≤
10 MHz)
0
1
0
Must not be
checked
1
(B)
→ (C) (X1 clock: 10 MHz < fXH ≤ 20 MHz)
1
0
1
0
Must be
checked
1
(B)
→ (C) (external main clock: 10 MHz < fXH ≤
20 MHz)
1
0
Must not be
checked
1
Unnecessary if these registers
are already set
Unnecessary if the
CPU is operating
with the high-speed
system clock
Note
The value of this flag can be changed only once after a reset release. This setting is not necessary if it has
already been set.
Caution
Set the clock after the supply voltage has reached the operable voltage of the clock to be set (see
CHAPTER 29
ELECTRICAL SPECIFICATIONS (STANDARD PRODUCTS) to CHAPTER 32
ELECTRICAL SPECIFICATIONS ((A2) GRADE PRODUCTS: TA =
40 to +125°C)).
(5) CPU clock changing from internal high-speed oscillation clock (B) to subsystem clock (D)
(Setting sequence of SFR registers)
Setting Flag of SFR Register
Status Transition
XTSTART
EXCLKS
OSCSELS
Waiting for
Oscillation
Stabilization
CSS
0
1
(B)
→ (D) (XT1 clock)
1
×
Necessary
1
(B)
→ (D) (external subsystem clock)
0
1
Unnecessary
1
Unnecessary if the CPU is operating
with the subsystem clock
Remarks 1. (A) to (I) in Table 6-5 correspond to (A) to (I) in Figure 6-14.
2. EXCLK, OSCSEL, EXCLKS, OSCSELS, AMPH:
Bits 7 to 4 and 0 of the clock operation mode select register (OSCCTL)
MSTOP:
Bit 7 of the main OSC control register (MOC)
XSEL, MCM0:
Bits 2 and 0 of the main clock mode register (MCM)
XTSTART, CSS: Bits 6 and 4 of the processor clock control register (PCC)
×:
Don’t care
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