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3-84
APPENDIX
7540 Group User’s Manual
3.3 Notes on use
When the ring oscillation is used as the operation clock, the CPU clock division ratio is the middle-
speed mode.
When the state transition state 2
→
state 3
→
state 4 is performed, execute the NOP instruction as
shown below according to the division ratio of CPU clock.
CPUM
76
→
10
2
(State 2
→
state 3)
NOP instruction
CPUM
4
→
1
2
(State 3
→
state 4)
Double-speed mode at ring oscillator: NOP
3
High-speed mode at ring oscillator: NOP
1
Middle-speed mode at ring oscillator: NOP
0
(6) Switch of ceramic and RC oscillations
After releasing reset the operation starts by starting a built-in ring oscillator. Then, a ceramic oscillation
or an RC oscillation is selected by setting bit 5 of the CPU mode register.
(7) Double-speed mode
When a ceramic oscillation is selected, a double-speed mode can be used. Do not use it when an
RC oscillation is selected.
(8) Clock division ratio, X
IN
oscillation control, ring oscillator control
The state transition shown in Figure 3.3.3 can be performed by setting the clock division ratio
selection bits (bits 7 and 6), X
IN
oscillation control bit (bit 4), ring oscillator oscillation control bit (bit
3) of CPU mode register. Be careful of notes on use in Figure 3.3.3.
Fig. 3.3.3 State transition
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←
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6
←
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2
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6
←
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2
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(
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CPUM
4
←
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2
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1
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State 2
Operation clock source:
f(X
IN
) (Note 1)
f(X
IN
) oscillation enabled
Ring oscillator enabled
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Notes on switch of clock
(1) In operation clock source = f(X
IN
), the following can be
selected for the CPU clock division ratio.
G
f(X
IN
)/2 (high-speed mode)
G
f(X
IN
)/8 (middle-speed mode)
G
f(X
IN
) (double-speed mode, only at a ceramic oscillation)
(2) Execute the state transition state 3 to state 2 or
state 3’ to state 2’ after stabilizing X
IN
oscillation.
(3) In operation clock source = ring oscillator, the middle-
speed mode is selected for the CPU clock division ratio.
(4) When the state transition state 2
→
state 3
→
state 4
is performed, execute the NOP instruction as shown below
according to the division ratio of CPU clock.
CPUM76
→
10
2
(State 2
→
state 3)
NOP instruction
CPUM4
→
1
2
(State 3
→
state 4)
Double-speed mode at ring oscillator: NOP
3
High-speed mode at ring oscillator: NOP
1
Middle-speed mode at ring oscillator: NOP
0
Reset state
C
P
U
M
7
6
←
1
0
2
CPUM
76
←
00
2
01
2
11
2
(Note 2)
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