Changing Setting Of Cpu Clock; Time Required For Switching Cpu Clock - NEC mPD780973 Series Preliminary User's Manual

6.6 Changing Setting of CPU Clock

6.6.1 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 (refer to Table 6-3).
Table 6-3. Maximum Time Required for Switching CPU Clock
Set Value
before Switching
PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0
PCC2 PCC1 PCC0
0
0 0 0
0 0 1 8 instructions
0 1 0 4 instructions
0 1 1 2 instructions
1 0 0 1 instruction
Remark One instruction is the minimum instruction execution time of the CPU clock before switching.
96
CHAPTER 6 CLOCK GENERATOR
Set Value after Switching
0 0 0 0 1
16 instructions
4 instructions
2 instructions
1 instruction
0 1 0 0 1
16 instructions 16 instructions
8 instructions 8 instructions
4 instructions
2 instructions
1 instruction 1 instruction
1 1 0 0
16 instructions
8 instructions
4 instructions
2 instructions