UPD780828A Datasheet, PDF (110/472 Pages) NEC – 8-bit Single-Chip Microcontroller

Chapter 5 Clock Generator
5.6 Changing System Clock and CPU Clock Settings
5.6.1 Time required for switchover between system clock and CPU clock
The system clock and CPU clock can be switched over by means of bit 0 to bit 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 contin-
ues on the pre-switchover clock for several instructions (see Table 5-2).
Table 5-2: Maximum Time Required for CPU Clock Switchover
Set Values after
Switchover
Set Values before Switchover
PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0
PCC2 PCC1 PCC0
000001010011100
000
8 instructions 4 instructions 2 instructions
1 instruction
0 0 1 16 instructions
4 instructions 2 instructions
1 instruction
0 1 0 16 instructions 8 instructions
2 instructions
1 instruction
0 1 1 16 instructions 8 instructions 4 instructions
1 instruction
1 0 0 16 instructions 8 instructions 4 instructions 2 instructions
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User’s Manual U16504EE1V1UD00