170CHAPTER 7 CLOCK GENERATORMCCCSSCLSMain System Clock OscillationSubsystem Clock OscillationCPU ClockLLOscillation does not stop.MCCCSSCLSMain System Clock OscillationSubsystem Clock OscillationCPU Clock7.5.1 Main system clock operationsWhen operated with the main system clock (with bit 5 (CLS) of the processor clock control register (PCC) set to0), the following operations are carried out by PCC setting.(a) Because the operation guarantee instruction execution speed depends on the power supply voltage, theminimum 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 oscillationdoes not stop. When bit 4 (CSS) of the PCC is set to 1 and the operation is switched to subsystem clockoperation (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
