MC9S08SG8 Datasheet, PDF (31/310 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 3
Modes of Operation
3.1 Introduction
The operating modes of the MC9S08SG8 are described in this chapter. Entry into each mode, exit from
each mode, and functionality while in each of the modes are described.
3.2 Features
• Active background mode for code development
• Wait mode — CPU shuts down to conserve power; system clocks are running and full regulation
is maintained
• Stop modes — System clocks are stopped and voltage regulator is in standby
— Stop3 — All internal circuits are powered for fast recovery
— Stop2 — Partial power down of internal circuits, RAM content is retained
3.3 Run Mode
This is the normal operating mode for the MC9S08SG8. This mode is selected upon the MCU exiting reset
if the BKGD/MS pin is high. In this mode, the CPU executes code from internal memory with execution
beginning at the address fetched from memory at 0xFFFE–0xFFFF after reset.
3.4 Active Background Mode
The active background mode functions are managed through the background debug controller (BDC) in
the HCS08 core. The BDC, together with the on-chip debug module (DBG), provide the means for
analyzing MCU operation during software development.
Active background mode is entered in any of the following ways:
• When the BKGD/MS pin is low during POR or immediately after issuing a background debug
force reset (see Section 5.7.2, “System Background Debug Force Reset Register (SBDFR)”)
• When a BACKGROUND command is received through the BKGD/MS pin
• When a BGND instruction is executed
• When encountering a BDC breakpoint
• When encountering a DBG breakpoint
After entering active background mode, the CPU is held in a suspended state waiting for serial background
commands rather than executing instructions from the user application program.
MC9S08SG8 MCU Series Data Sheet, Rev. 0
Freescale Semiconductor
PRELIMINARY
31