CHAPTER 6 CLOCK GENERATION FUNCTION
User’s Manual U13850EJ4V0UM
161
Cautions 1. While CLKOUT is output, do not change the CPU clock (the value of the CK2 to CK0 in the
PCC register).
2. Even if the MCK bit is set to 1 during main clock operation, the main clock is not stopped.
The CPU clock stops after the sub clock is selected.
Remark
X: don’t care
(a) Example of main clock operation
→
→
→
→
sub clock operation setup
<1> CK2
←
1:
Bit manipulation instructions are recommended. Do not change CK1 and CK0.
<2> Sub clock operation: The maximum number of the following instructions is required before sub clock
operation after the CK2 bit is set.
(CPU clock frequency before setting / sub clock frequency)
×
2
Therefore, insert the wait described above using a program.
<3> MCK
←
1:
Only when the main clock is stopped.
(b) Example of sub clock operation
→
→
→
→
main clock operation setup
<1> MCK
←
0:
Main clock oscillation start
<2> Insert wait using a program and wait until the main clock oscillation stabilizing time elapses.
<3> CK2, CK1, CH0
←
CPU clock
<4> Main clock operation: If CK1 and CH0 are not changed from value of the CPU clock selected before
the sub clock operation, a maximum of two instructions is required.
If CK1 and CK0 are changed, a maximum of ten instructions is required