IBM nec pd78082 User Manual
77
CHAPTER 5 CLOCK GENERATOR
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).
Table 5-2. Maximum Time Required for CPU Clock Switchover
1
0
0
1
1
0
1
0
0
1
0
0
0
0
0
PCC0
PCC2 PCC1
0
0
0
0
1
1
0
0
0
1
1
1
8 instructions
2 instructions
4 instructions
4 instructions
2 instructions
8 instructions
4 instructions
4 instructions
2 instructions
8 instructions
8 instructions
2 instructions
Set Values After Switchover
Set Values before
Switchover
Switchover
1 instruction
1 instruction
1 instruction
PCC1
PCC2
PCC0
PCC1
PCC2
PCC0
PCC1
PCC2
PCC0
PCC1
PCC2
PCC0
PCC1
PCC2
PCC0
1 instruction
Remark
One instruction is the minimum instruction execution time with the pre-switchover CPU clock.
0
0
0
16 instructions
16 instructions
16 instructions
16 instructions