NXP Semiconductors MC9S08QL4, Reference Manual

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Chapter 3 Modes of Operation
MC9S08QL8 MCU Series Reference Manual, Rev. 1
NXP Semiconductors 27
• Non-intrusive commands, defined as commands that can be issued while the user program is
running. Non-intrusive commands 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
— BDC register access commands
— The BACKGROUND command
• Active background commands, which can only be executed while the MCU is in active background
mode. Active background commands 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)
The active background mode is used to program a bootloader or user application program into the flash
program memory before the MCU is operated in run mode for the first time. When the MC9S08QL8 series
are shipped from the NXP Semiconductors factory, the flash program memory is erased by default unless
specifically noted. As a result, 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 has been previously programmed.
For additional information about the active background mode, refer to the Chapter 16, 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 I bit in CCR is cleared when the CPU enters the
wait mode, enabling interrupts. When an interrupt request occurs, the CPU exits the wait mode and
resumes processing, beginning with the stacking operations that lead to the interrupt service routine.
While the MCU is in wait mode, there are some restrictions on which 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.
3.5.1 Low Power Wait Mode (LPWait)
Low power wait mode is entered by executing a WAIT instruction while the MCU is in low power run
mode. In the low power wait mode, the on-chip voltage regulator remains in its standby state (as in the low
power run mode). This state uses the minimum power consumption necessary for most modules to
maintain functionality. Power consumption is most reduced by disabling the clocks to all unused
peripherals by clearing the corresponding bits in the SCGC register.
The same restrictions on the low power run mode apply to low power wait mode.