MC9RS08KA8RM Datasheet, PDF (26/190 Pages) Freescale Semiconductor, Inc – MC9RS08KA8 Features

Chapter 3 Modes of Operation
• When a BDC breakpoint is encountered
After active background mode is entered, the CPU stays in a suspended state waiting for serial background
commands rather than executing instructions from the user application program.
Background commands are of two types:
• Non-intrusive commands — Commands that can be issued while the user program is running, can
be issued through the BKGD pin while the MCU is in run mode. Non-intrusive commands can also
be executed when the MCU is in the active background mode. Non-intrusive commands include:
— Memory access commands
— Memory-access-with-status commands
— BACKGROUND command
• Active background commands — Can be executed only while the MCU is in active background
mode, include commands to:
— Read or write CPU registers
— Trace one user program instruction at a time
— Leave active background mode to return to the user application program (GO)
Active background mode is used to program user application code into the flash program memory before
the MCU is operated in run mode for the first time. When the MC9RS08KA8 series is shipped, the flash
program memory is usually erased so no program can be executed in run mode until the flash memory is
initially programmed. The active background mode can also be used to erase and reprogram the flash
memory after it is programmed.
For additional information about active background mode, refer to the Chapter 15, “Development
Support.”
3.5 Wait Mode
Wait mode is entered by executing a WAIT instruction. Upon execution of the WAIT instruction, the CPU
enters a low-power state in which it is not clocked. The program counter (PC) is halted at the position
where the WAIT instruction executes. When an interrupt request occurs:
1. MCU exits wait mode and resumes processing.
2. PC is incremented by one and fetches the next instruction to be processed.
The user program must probe the corresponding interrupt source that woke the MCU because no vector
fetching process is involved.
While the MCU is in wait mode, not all background debug commands can be used. Only the
BACKGROUND command and memory-access-with-status commands are available. The
memory-access-with-status commands do not allow memory access, but they report an error indicating
that the MCU is in stop or wait mode. The BACKGROUND command can be used to wake the MCU from
wait mode and enter active background mode.
MC9RS08KA8 Series Reference Manual, Rev. 3
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