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CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U14581EJ3V0UM00
5.6 Changing Setting of CPU Clock
5.6.1 Time required for switching CPU clock
The CPU clock can be selected by using bits 0 to 2 (PCC0 to PCC2) of the processor clock control register (PCC).
Actually, the specified clock is not selected immediately after the setting of PCC has been changed, and the old
clock is used for the duration of several instructions after that (see Table 5-3).
Table 5-3. Maximum Time Required for Switching CPU Clock
Set Value after Switching
PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0
PCC2 PCC1 PCC0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
0
0
0
16 instructions
16 instructions
16 instructions
16 instructions
0
0
1
8 instructions
8 instructions
8 instructions
8 instructions
0
1
0
4 instructions
4 instructions
4 instructions
4 instructions
0
1
1
2 instructions
2 instructions
2 instructions
2 instructions
1
0
0
1 instruction
1 instruction
1 instruction
1 instruction
Remark
One instruction is the minimum instruction execution time of the CPU clock before switching.
Set Value
before Switching
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