
CHAPTER 6 CLOCK GENERATION FUNCTION
User’s Manual U15905EJ2V1UD
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6.3
Control Registers
(1) Processor clock control register (PCC)
The processor clock control register (PCC) is a special register. Data can be written to it only in combination of
specific sequences (refer to 3.4.8 Special registers).
This register can be read or written in 8-bit or 1-bit units. The CLS bit is a read-only bit.
FRC
Used
Not used
FRC
0
1
Selects internal feedback resistor of subclock
PCC
MCK
MFRC
CLSNote
CK3
CK2
CK1
CK0
Operating
Stopped
MCK
0
1
Operation of main clock
Used
Not used
MFRC
0
1
Selects internal feedback resistor of main clock
After reset: 03H
R/W
Address: FFFFF828H
Main clock operation
Subclock operation
CLS
0
1
Status of CPU clock (fCPU)
fXX
fXX/2
fXX/4
fXX/8
fXX/16
fXX/32
Setting prohibited
fXT (subclock: 32.768 kHz)
CK2
0
1
X
Selects clock (fCLK/fCPU)
CK1
0
1
0
1
X
CK0
0
1
0
1
0
1
X
CK3
0
1
Even if the MCK bit is set to 1 while the system is operating with the main clock as
the CPU clock, the operation of the main system clock does not stop. It stops after
the CPU clock has been changed to the subclock.
When the main clock is stopped and the device is operating on the subclock, clear
the MCK bit to 0 and wait until the oscillation stabilization time has been secured
by the program before switching back to the main clock.
<6>
<4>
<3>
Note
The CLS bit is a read-only bit.
Caution
Do not change the CPU clock (by using the CK2 to CK0 bits of the PCC register) while
CLKOUT is being output.
Remark
X: Don’t care.