SC9RS08KA2 datasheet(22/134 Pages) FREESCALE

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Chapter 3 Modes of Operation

SC9RS08KA2 Series Data Sheet, Rev. 1

Freescale Semiconductor

•

When a BDC breakpoint is encountered

After active background mode is entered, the CPU is held 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, defined as 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, which 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 SC9RS08KA2 Series is shipped from the

Freescale Semiconductor factory, the Flash program memory is usually erased so there is no program that

could 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 has been previously programmed.

For additional information about the active background mode, refer to the Development Support chapter

of this data sheet.

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 is executed. 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.

It is the responsibility of the user program to 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 when the MCU is in

wait mode. The memory-access-with-status commands do not allow memory access, but they report an

error indicating that the MCU is in either stop or wait mode. The BACKGROUND command can be used

to wake the MCU from wait mode and enter active background mode.

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