M16C62P_06 Datasheet, PDF (119/421 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/60 SERIES

M16C/62P Group (M16C/62P, M16C/62PT)
10. Clock Generation Circuit
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
and low voltage detection 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 to Switch
Clock Source From On-chip Oscillator to 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 function 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”.
Switch the main clock
NO
Determine several times whether
the CM23 bit is set to “0”
(main clock oscillates)
YES
Set the CM06 bit to “1”
(divide-by-8)
Set the CM22 bit to “0”
(main clock does not stop)
Set the CM21 bit to “0”
(main clock as CPU clock source)⁽¹⁾
End
CM06 bit : Bit in CM0 register
CM21 to CM23 bits : Bits in CM2 register
NOTES:
1. If the clock source for CPU clock is to be changed to PLL clock, set to PLL operation mode
after set to high-speed mode.
Figure 10.12 Procedure to Switch Clock Source From On-chip Oscillator to Main Clock
Rev.2.41 Jan 10, 2006 Page 104 of 390
REJ09B0185-0241