Ibm uPD78082 Manuel d'utilisateur Page 100

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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
100110100100000
PCC0PCC2 PCC1
0
00
011
00
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
1 instruction 1 instruction1 instruction
PCC1PCC2 PCC0PCC1PCC2 PCC0PCC1PCC2 PCC0PCC1PCC2 PCC0PCC1PCC2 PCC0
1 instruction
Remark One instruction is the minimum instruction execution time with the pre-switchover CPU clock.
000 16 instructions 16 instructions 16 instructions 16 instructions
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