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Freescale Semiconductor
Application Note
Document Number: AN3387
Rev. 0, 10/2007
Contents
© Freescale Semiconductor, Inc., 2006. All rights reserved.
1 Introduction
Microcontroller (MCU) based electronic-control units
(ECU) are rapidly replacing mechanical and passive
electronic systems in automobiles. Each ECU node
demands current from the electrical system even when
the engine is not running, leaving the battery as the only
source of power. ECU designers face the challenge of
adding more functionality to the vehicle while keeping
the total key-off current demand below the fixed limit of
the battery’s available energy.
This application note focuses on using the S08DZ MCU
to achieve low power consumption. The S08DZ is a
member of the high-performance HCS08 family of 8-bit
microcontrollers. Common family features include a
40 MHz HCS08 CPU, an enhanced instruction set,
controller area network (CAN), and a background-debug
controller (BDC) that provides an easy interface for
in-system, real-time debugging. See the device data
sheet, Freescale document MC9S08DZ60, for a more
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 System Clock Generation . . . . . . . . . . . . . . . . . . . . . . . . 2
3 Operation Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1 Real-Time Counter (RTC) . . . . . . . . . . . . . . . . . . . . 4
3.2 Low-Voltage Detect (LVD). . . . . . . . . . . . . . . . . . . . 4
3.3 Operating Voltage Ranges . . . . . . . . . . . . . . . . . . . 4
3.4 Internal Voltage Regulator. . . . . . . . . . . . . . . . . . . . 4
4 Description of Low-Power Modes . . . . . . . . . . . . . . . . . . 4
4.1 Stop Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2 Stop2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3 Stop3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4 Wait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.5 Using the Low-Power Modes. . . . . . . . . . . . . . . . . . 6
4.6 Using Stop2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.7 Using Stop3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5 Demonstration Software . . . . . . . . . . . . . . . . . . . . . . . . . 9
HCS08 Automotive Low-Power
Modes
by: Matt Ruff
Automotive Systems Engineering
Austin, TX
