M16CSLASH62P datasheet(74/349 Pages) MITSUBISHI

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Clock Generation Circuit

Mitsubishi microcomputers

M16C / 62P Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Under

development

Preliminary Specifications Rev.1.0

Specifications in this manual are tentative and subject to change.

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 inter-

rupt. If the 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, return the main clock to the CPU clock and

peripheral function clock source in the program. Figure 1.9.12 shows the procedure for switching the

clock source from the ring oscillator to the main clock.

• Simultaneously with oscillation stop, re-oscillation detection interrupt occurrence, the CM22 bit be-

comes “1”. When the CM22 bit is set at “1”, oscillation stop, re-oscillation detection interrupt are dis-

abled. 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-oscilla-

tion detection interrupt request is generated. At the same time, the ring 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 ring 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 dis-

abled) 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”.

Figure 1.9.12. Procedure to Switch Clock Source From Ring Oscillator to Main Clock

Main clock switch

Inspect the CM23 bit

Do this check a number of times

Set the CM22 bit to 0 (main clock stop,

re-oscillation not detected).

Set the CM21 bit to 0

(main clock for the CPU clock source)(Note)

1(Main clock stop)

0(Main clock oscillation)

The main clock is confirmed to be active a number of times.

All of CM21-23 are the CM2 register bits

End

Note: 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.

M16C/62P Datasheet(PDF) 74 Page - Mitsubishi Electric Semiconductor

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