Datasheet

Section 5 Clock Pulse Generator
Rev. 3.00 Sep. 10, 2007 Page 79 of 528
REJ09B0216-0300
5.3 System Clock Select Operation
Figure 5.2 shows the state transition of the system clock.
Reset state
LSI operates on on-chip oscillator clock
On-chip oscillator: Operated
External oscillator: Halted
Switching to
external clock
On-chip oscillator: Halted
External oscillator: Operated
On-chip oscillator: Operated
External oscillator: Operated
Oscillator halted
Oscillator operated
LSI operates on external oscillator
Reset release
Note: * Conditions for the state transition are as follows:
• When the external oscillator halt is detected while the backup function is enabled
• When the external clock is switched to the on-chip oscillator clock by user software
while the backup function is disabled
*
Figure 5.2 State Transition of System Clock
5.3.1 Clock Control Operation
The LSI system clock is generated by the on-chip oscillator clock after a reset. The system clock
sources are switched from the on-chip oscillator to the external clock by the user software. Figure
5.3 shows the flowchart to switch clocks with the external clock backup function enabled. Figures
5.4 and 5.5 show the flowcharts to switch clocks with the external clock backup function disabled.