CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U19014EJ1V0UD
89
(5) Main clock mode register (MCM)
This register selects the main system clock supplied to CPU clock and clock supplied to peripheral hardware
clock.
MCM can be set by a 1-bit or 8-bit memory manipulation instruction.
Reset signal generation sets this register to 00H.
Figure 5-6. Format of Main Clock Mode Register (MCM)
Address: FFA1H After reset: 00H R/W
Note
Symbol
7 6 5 4 3
<2>
<1>
<0>
MCM
0 0 0 0 0
XSEL
MCS
MCM0
Selection of clock supplied to main system clock and peripheral hardware
XSEL MCM0
Main system clock (f
XP
)
Peripheral hardware clock (f
PRS
)
0 0
0 1
Internal high-speed oscillation clock
(f
RH
)
Internal high-speed oscillation clock
(f
RH
)
1 0
Setting
prohibited
1
1
High-speed system clock (f
XH
)
High-speed system clock (f
XH
)
MCS
Main system clock status
0
Operates with internal high-speed oscillation clock
1
Operates
with
high-speed system clock
Note
Bit 1 is read-only.
Cautions 1. XSEL can be changed only once after a reset release.
2. Be sure to set XSEL=1, MCM0=1 if using the USB function.
3.
A clock other than f
PRS
is supplied to the following peripheral functions
regardless of the setting of XSEL and MCM0.
•
Watchdog timer (operates with internal low-speed oscillation clock)
•
When “f
RL
”, “f
RL
/2
7
”, or “f
RL
/2
9
” is selected as the count clock for 8-bit timer H1
(operates with internal low-speed oscillation clock)
•
Peripheral hardware selects the external clock as the clock source
(Except when the external count clock of TM00 is selected (TI000 pin valid
edge))
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