MC68HC05P4A Datasheet, PDF (29/72 Pages) Advanced Analogic Technologies – Microcontrollers

Chapter 6
Low-Power Modes
6.1 Introduction
The MC68HC05P4A is capable of running in a low-power mode in each of its configurations. The WAIT
and STOP instructions provide two modes that reduce the power required for the MCU by stopping
various internal clocks and/or the on-chip oscillator. The STOP and WAIT instructions are not normally
used if the computer operating properly (COP) watchdog timer is enabled. The flow of the stop and wait
modes is shown in Figure 6-1.
6.2 Stop Mode
Execution of the STOP instruction places the MCU in its lowest power consumption mode. In stop mode,
the internal oscillator is turned off, halting all internal processing, including the COP watchdog timer.
Execution of the STOP instruction automatically clears the I bit in the condition code register so that the
IRQ external interrupt is enabled. All other registers and memory remain unaltered. All input/output lines
remain unchanged.
The MCU can be brought out of stop mode only by an IRQ external interrupt or an externally generated
RESET. When exiting the stop mode, the internal oscillator will resume after a 4064 PH2 clock cycle
oscillator stabilization delay.
6.3 WAIT Instruction
The WAIT instruction places the MCU in a low-power mode, which consumes more power than stop
mode. In wait mode, the PH2 clock is halted, suspending all processor and internal bus activity. Internal
timer clocks remain active, permitting interrupts to be generated from the 16-bit timer and reset to be
generated from the COP watchdog timer. Execution of the WAIT instruction automatically clears the I bit
in the condition code register enabling the IRQ external interrupt. All other registers, memory, and
input/output lines remain in their previous state.
If the 16-bit timer interrupt is enabled, it will cause the processor to exit wait mode and resume normal
operation. The 16-bit timer may be used to generate a periodic exit from wait mode. The wait mode may
also be exited when an IRQ external interrupt or RESET occurs.
MC68HC05P4A Data Sheet, Rev. 7.1
Freescale Semiconductor
29