MC908GR32AVFAE Datasheet, PDF (121/314 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10
Low-Power Modes
10.1 Introduction
The microcontroller (MCU) may enter two low-power modes: wait mode and stop mode. They are
common to all HC08 MCUs and are entered through instruction execution. This section describes how
each module acts in the low-power modes.
10.1.1 Wait Mode
The WAIT instruction puts the MCU in a low-power standby mode in which the central processor unit
(CPU) clock is disabled but the bus clock continues to run. Power consumption can be further reduced by
disabling the low-voltage inhibit (LVI) module through bits in the CONFIG1 register. See Chapter 5
Configuration Register (CONFIG).
10.1.2 Stop Mode
Stop mode is entered when a STOP instruction is executed. The CPU clock is disabled and the bus clock
is disabled if the OSCENINSTOP bit in the CONFIG2 register is a 0. See Chapter 5 Configuration Register
(CONFIG).
10.2 Analog-to-Digital Converter (ADC)
10.2.1 Wait Mode
The analog-to-digital converter (ADC) continues normal operation during wait mode. Any enabled CPU
interrupt request from the ADC can bring the MCU out of wait mode. If the ADC is not required to bring
the MCU out of wait mode, power down the ADC by setting ADCH4–ADCH0 bits in the ADC status and
control register before executing the WAIT instruction.
10.2.2 Stop Mode
The ADC module is inactive after the execution of a STOP instruction. Any pending conversion is aborted.
ADC conversions resume when the MCU exits stop mode after an external interrupt. Allow one
conversion cycle to stabilize the analog circuitry.
10.3 Break Module (BRK)
10.3.1 Wait Mode
The break (BRK) module is active in wait mode. In the break routine, the user can subtract one from the
return address on the stack if the SBSW bit in the break status register is set.
10.3.2 Stop Mode
The break module is inactive in stop mode. The STOP instruction does not affect break module register
states.
MC68HC908GR60A • MC68HC908GR48A • MC68HC908GR32A Data Sheet, Rev. 5
Freescale Semiconductor
121