M37733MHBXXXFP Datasheet, PDF (59/89 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

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Note that the port-XC selection bit cannot be cleared by software
when it is once set to “1”. The bit can be cleared only by reset. It is
impossible to write “1” to the port-XC selection bit and the system
clock selection bit at the same time. In addition, the contents of the
main clock stop bit and the XCOUT drivability selection bit cannot be
changed when the port-XC selection bit is “0”.
Figure 67 shows the system clock selection change example when
using the sub clock. When the system clock selection bit is “1” after
sub-clock oscillation starts, the sub clock is selected as the system
clock. Make sure to select the sub clock after the sub-clock oscillation
is fully stabilized.
When the main clock stop bit is set to “1” after the sub clock is selected,
the main-clock oscillation/input stops. By stopping the main-clock
oscillation, current consumption can be further restricted.
When the main clock stop bit is cleared to “0” after the main-clock
oscillation stops, the main-clock oscillation/input restarts.
When the system clock selection bit is “0” after the main-clock
oscillation restarts, the main clock is selected as the system clock
again. Make sure to select the main clock after the main-clock
oscillation restarts and is fully stabilized.
The XCOUT drivability selection bit is a bit to select the drivability of
the sub-clock oscillation circuit and is set to “1” (HIGH) after reset is
released. Make sure to clear the XCOUT drivability selection bit to “0”
(LOW) after the sub-clock oscillation is fully stabilized.
MITSUBISHI MICROCOMPUTERS
M37733MHBXXXFP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Port-Xc selection bit (CM4)
System colck selection bit (CM3)
Main clock stop bit (CM2)
System clock
Main-clock oscillation
Sub-clock oscillation
Main clock
Sub clock
Main clock
Operating
Oscillation stabilizing time
Stop
Operating
Stopped
Oscillation stabilizing time
Operating
Fig. 67 System clock selection change example
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