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CHAPTER 7 CLOCK GENERATOR
MCC
CSS
CLS
Main System Clock Oscillation
Subsystem Clock Oscillation
CPU Clock
L
L
Oscillation does not stop.
MCC
CSS
CLS
Main System Clock Oscillation
Subsystem Clock Oscillation
CPU Clock
7.5.1 Main system clock operations
When operated with the main system clock (with bit 5 (CLS) of the processor clock control register (PCC) set to
0), the following operations are carried out by PCC setting.
(a) Because the operation guarantee instruction execution speed depends on the power supply voltage, the
minimum instruction execution time can be changed by bits 0 to 2 (PCC0 to PCC2) of the PCC.
(b) If bit 7 (MCC) of the PCC is set to 1 when operated with the main system clock, the main system clock oscillation
does not stop. When bit 4 (CSS) of the PCC is set to 1 and the operation is switched to subsystem clock
operation (CLS = 1) after that, the main system clock oscillation stops (see Figure 7-9).
Figure 7-9. Main System Clock Stop Function (1/2)
(a) Operation when MCC is set after setting CSS with main system clock operation
(b) Operation when MCC is set in case of main system clock operation