116
CHAPTER 5 CLOCK GENERATOR
User’s Manual U15798EJ2V0UD
Figure 5-3. Format of Processor Clock Control Register (PCC)
Address: FFFBH After reset: 04H R/W
Note 1
Symbol
7
6
5
4
3
2
1
0
PCC
MCC
FRC
CLS
CSS
0
PCC2
PCC1
PCC0
MCC
Main system clock oscillation control
Note 2
0
Oscillation possible
1
Oscillation stopped
FRC
Subsystem clock feedback resistor selection
0
Internal feedback resistor used
1
Internal feedback resistor not used
Note 3
CLS
CPU clock status
0
Main system clock
1
Subsystem clock
CSS
PCC2
PCC1
PCC0
CPU clock (f
CPU
) selection
0
0
0
0
f
X
0
0
1
f
X
/2
0
1
0
f
X
/2
2
0
1
1
f
X
/2
3
1
0
0
f
X
/2
4
1
0
0
0
f
XT
/2
0
0
1
2f
XT
(when
×
4 circuit is used)
0
1
0
0
1
1
1
0
0
Other than above
Setting prohibited
Notes 1.
Bit 5 is a read-only bit.
2.
When the CPU is operating on the subsystem clock, MCC should be used to stop the main system clock
oscillation. A STOP instruction should not be used.
3.
FRC can be set to 1 only when the subsystem clock is not used.
Cautions 1. Be sure to set bit 3 to 0.
2. When the external clock is input, MCC should not be set. This is because the X2 pin is
connected to V
DD1
via a pull-up resistor.
3. If the clock must be switched over between the subsystem clock being used in
×
4 mode and
the main system clock, be sure to set the CPU clock frequency when the main system clock
is used to 280 kHz or more.
Remarks 1.
f
X
:
Main system clock oscillation frequency
2.
f
XT
: Subsystem clock oscillation frequency
Содержание mPD780344 Series
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