MC68HC05L16 Datasheet, PDF (47/146 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 5
Low-Power Modes
5.1 Introduction
The MCU has two power-saving modes, stop and wait. Flowcharts of these modes are shown in
Figure 5-2.
5.2 Stop Mode
The STOP instruction places the MCU in its lowest-power mode. In stop mode, the internal main oscillator
OSC is turned off, halting all internal processing, including timer operations (timer 1, timer 2, and
computer operating properly (COP) watchdog timer). Suboscillator XOSC does not stop oscillating.
Therefore, if XOSC is used as the clock source for the COP watchdog timer, COP is still functional in stop
mode. See Chapter 7 Oscillators/Clock Distributions.
During stop mode, the timer prescaler is cleared. The I bit in the condition code register (CCR) is cleared
to enable external interrupts. All other registers and memory remain unaltered. All input/output lines
remain unchanged. The processor can be brought out of stop mode only by RESET or an interrupt from
IRQ1, IRQ2, KWI, SSPI (slave mode only), or TBI. See Chapter 7 Oscillators/Clock Distributions.
5.3 Wait Mode
The WAIT instruction places the MCU in a low-power mode, but wait mode consumes more power than
stop mode. All CPU action is suspended, but on-chip peripherals and oscillators remain active. Any
interrupt or reset (including a COP reset) will cause the MCU to exit wait mode.
During wait mode, the I bit in the CCR is cleared to enable interrupts. All other registers, memory, and
input/output lines remain in their previous state. The timers may be enabled to allow a periodic exit from
wait mode. Wait mode must be exited and the COP must be reset to prevent a COP timeout.
The reduction of power in wait mode depends on how many of the on-chip peripheral's clocks can be shut
down. Therefore, the amount of power that will be consumed is dependent on the application, and it would
be prohibitive to test all parts for all variations. For these reasons, the values given in Chapter 12 Electrical
Specifications reflect typical application conditions after initial characterization of silicon.
MC68HC05L16 • MC68HC705L16 Data Sheet, Rev. 4.1
Freescale Semiconductor
47