Changing Cpu Clock Settings; Time Required For Cpu Clock Switchover; Maximum Time Required For Cpu Clock Switchover - NEC PD78081(A) User Manual

5.6 Changing CPU Clock Settings

5.6.1 Time required for CPU clock switchover

The CPU clock can be switched over by means of bits 0 to 2 (PCC0 to PCC2) of the processor clock control register
(PCC).
The actual switchover operation is not performed directly after writing to the PCC, but operation continues on the
pre-switchover clock for several instructions (see Table 5-2).
Set Values before
Switchover
PCC2
PCC2 PCC1 PCC0
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
Remark One instruction is the minimum instruction execution time with the pre-switchover CPU clock.
CHAPTER 5 CLOCK GENERATOR
Table 5-2. Maximum Time Required for CPU Clock Switchover
PCC1 PCC0 PCC2 PCC1
0 0 0 0
16 instructions
8 instructions
4 instructions 4 instructions
2 instructions 2 instructions
1 instruction 1 instruction
Set Values After Switchover
PCC0 PCC2 PCC1 PCC0
0 1 0 1
16 instructions
8 instructions
2 instructions
1 instruction
PCC2 PCC1 PCC0 PCC2
0 0 1 1
16 instructions
8 instructions
4 instructions
1 instruction
PCC1 PCC0
1 0 0
16 instructions
8 instructions
4 instructions
2 instructions
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