MC68HC908GR4MP datasheet(38/286 Pages) FREESCALE

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Low-Power Modes

MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

Freescale Semiconductor

3.3 Break Module (BRK)

3.3.1 Wait Mode

If enabled, the break module is active in wait mode. In the break routine, the user can subtract one from

the return address on the stack if the BW bit in the break status register is set.

3.3.2 Stop Mode

The break module is inactive in stop mode. The STOP instruction does not affect break module register

states.

3.4 Central Processor Unit (CPU)

3.4.1 Wait Mode

The WAIT instruction:

•

Clears the interrupt mask (I bit) in the condition code register, enabling interrupts. After exit from

wait mode by interrupt, the I bit remains clear. After exit by reset, the I bit is set.

•

Disables the CPU clock

3.4.2 Stop Mode

The STOP instruction:

•

Clears the interrupt mask (I bit) in the condition code register, enabling external interrupts. After

exit from stop mode by external interrupt, the I bit remains clear. After exit by reset, the I bit is set.

•

Disables the CPU clock

After exiting stop mode, the CPU clock begins running after the oscillator stabilization delay.

3.5 Clock Generator Module (CGM)

3.5.1 Wait Mode

The CGM remains active in wait mode. Before entering wait mode, software can disengage and turn off

the PLL by clearing the BCS and PLLON bits in the PLL control register (PCTL). Less power-sensitive

applications can disengage the PLL without turning it off. Applications that require the PLL to wake the

MCU from wait mode also can deselect the PLL output without turning off the PLL.

3.5.2 Stop Mode

If the OSCSTOPEN bit in the CONFIG register is cleared (default), then the STOP instruction disables

the CGM (oscillator and phase-locked loop) and holds low all CGM outputs (CGMXCLK, CGMOUT, and

CGMINT).

If the OSCSTOPEN bit in the CONFIG register is set, then the phase locked loop is shut off, but the

oscillator will continue to operate in stop mode.

MC68HC908GR4MP Datasheet(PDF) 38 Page - Freescale Semiconductor, Inc