Renesas M16C/6NK Información técnica descargar pdf (Pagina 102)

Rev.2.10 Apr 14, 2006 page 78 of 378

REJ09B0124-0210

M16C/6N Group (M16C/6NK, M16C/6NM) 8. Clock Generation Circuit

8.5 Oscillation Stop and Re-oscillation Detection Function

The oscillation stop and re-oscillation detection function is such that main clock oscillation circuit stop and

re-oscillation are detected. At oscillation stop, re-oscillation detection, reset or oscillation stop, re-oscillation

detection interrupt request are generated. Which is to be generated can be selected using the CM27 bit in

the CM2 register.

The oscillation stop and re-oscillation detection function can be enabled and disabled using the CM20 bit in

the CM2 register.

Table 8.9 lists a Specification Overview of Oscillation Stop and Re-oscillation Detection Function.

Table 8.9 Specification Overview of Oscillation Stop and Re-oscillation Detection Function

Item Specification

Oscillation stop detectable clock and f(XIN) ≥ 2 MHz

frequency bandwidth

Enabling condition for oscillation stop Set CM20 bit to 1 (enabled)

and re-oscillation detection function

Operation at oscillation stop, •Reset occurs (when CM27 bit = 0)

re-oscillation detection •

Oscillation stop, re-oscillation detection interrupt is generated (when CM27 bit =1)

8.5.1 Operation when CM27 Bit = 0 (Oscillation Stop Detection Reset)

Where main clock stop is detected when the CM20 bit is 1 (oscillation stop, re-oscillation detection function

enabled), the MCU is initialized, coming to a halt (oscillation stop reset; refer to 4. Special Function

Registers (SFRs), 5. Resets).

This status is reset with hardware reset. Also, even when re-oscillation is detected, the MCU can be

initialized and stopped; it is, however, necessary to avoid such usage (During main clock stop, do not set

the CM20 bit to 1 and the CM27 bit to 0).

8.5.2 Operation when CM27 Bit = 1 (Oscillation Stop, Re-oscillation Detection Interrupt)

Where the main clock corresponds to the CPU clock source and the CM20 bit is 1 (oscillation stop, re-oscillation

detection function enabled), the system is placed in the following state if the main clock comes to a halt:

• Oscillation stop, re-oscillation detection interrupt request is generated.

• The on-chip oscillator starts oscillation, and the on-chip oscillator clock becomes the clock source for

CPU clock and peripheral functions in place of the main clock.

• CM21 bit = 1 (on-chip oscillator clock is the clock source for CPU clock)

• CM22 bit = 1 (main clock stop detected)

• CM23 bit = 1 (main clock stopped)

Where the PLL clock corresponds to the CPU clock source and the CM20 bit is 1, the system is placed in

the following state if the main clock comes to a halt: Since the CM21 bit remains unchanged, set it to 1

(on-chip oscillator clock) inside the interrupt routine.

• Oscillation stop, re-oscillation detection interrupt request is generated.

• CM22 bit = 1 (main clock stop detected)

• CM23 bit = 1 (main clock stopped)

• CM21 bit remains unchanged

Where the CM20 bit is 1, the system is placed in the following state if the main clock re-oscillates from the

stop condition:

• Oscillation stop, re-oscillation detection interrupt request is generated.

• CM22 bit = 1 (main clock re-oscillation detected)

• CM23 bit = 0 (main clock oscillation)

• CM21 bit remains unchanged

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Renesas M16C/6NK Información técnica Pagina 102

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