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M16C/62P Group (M16C/62P, M16C/62PT)
10.6.3 How to Use Oscillation Stop and Re-oscillation Detect Function
• The oscillation stop and re-oscillation detect interrupt shares the vector with the watchdog timer
interrupt. If the oscillation stop, re-oscillation detection and watchdog timer interrupts both are
used, read the CM22 bit in an interrupt routine to determine which interrupt source is requesting
the interrupt.
• Where the main clock re-oscillated after oscillation stop, the clock source for the CPU clock and
peripheral functions must be switched to the main clock in the program. Figure 10.12 shows the
procedure for switching the clock source from the on-chip oscillator to the main clock.
• Simultaneously with oscillation stop, re-oscillation detection interrupt occurrence, the CM22 bit
becomes "1". When the CM22 bit is set at "1," oscillation stop, re-oscillation detection interrupt are
disabled. By setting the CM22 bit to "0" in the program, oscillation stop, re-oscillation detection
interrupt are enabled.
• If the main clock stops during low speed mode where the CM20 bit is "1," an oscillation stop, re-
oscillation detection interrupt request is generated. At the same time, the on-chip oscillator starts
oscillating. In this case, although the CPU clock is derived from the sub clock as it was before the
interrupt occurred, the peripheral function clocks now are derived from the on-chip oscillator clock.
• To enter wait mode while using the oscillation stop, re-oscillation detection function, set the CM02
bit to "0" (peripheral function clocks not turned off during wait mode).
• Since the oscillation stop, re-oscillation detection function is provided in preparation for main clock
stop due to external factors, set the CM20 bit to "0" (Oscillation stop, re-oscillation detection func-
tion disabled) where the main clock is stopped or oscillated in the program, that is where the stop
mode is selected or the CM05 bit is altered.
• This function cannot be used if the main clock frequency is 2 MHz or less. In that case, set the
CM20 bit to "0".
NOTES:
1. If the clock source for CPU clock is to be changed to PLL clock, set to PLL operation
Figure 10.12 Procedure to Switch Clock Source From On-chip Oscillator to Main Clock
page 87
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Switch the
mode after set to high-speed mode.
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mode T 37TD0u
10. Clock Generating Circuit
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