MC9S08GB60 Datasheet, PDF (251/290 Pages) Motorola, Inc – Microcontrollers

Registers and Control Bits
CLKSW — Select Source for BDC Communications Clock
CLKSW defaults to 0, which selects the alternate BDC clock source.
1 = MCU bus clock.
0 = Alternate BDC clock source.
WS — Wait or Stop Status
When the target CPU is in wait or stop mode, most BDC commands cannot function. However, the
BACKGROUND command can be used to force the target CPU out of wait or stop and into active
background mode where all BDC commands work. Whenever the host forces the target MCU into
active background mode, the host should issue a READ_STATUS command to check that
BDMACT = 1 before attempting other BDC commands.
1 = Target CPU is in wait or stop mode, or a BACKGROUND command was used to change from
wait or stop to active background mode.
0 = Target CPU is running user application code or in active background mode (was not in wait or
stop mode when background became active).
WSF — Wait or Stop Failure Status
This status bit is set if a memory access command failed due to the target CPU executing a wait or stop
instruction at or about the same time. The usual recovery strategy is to issue a BACKGROUND
command to get out of wait or stop mode into active background mode, repeat the command that failed,
then return to the user program. (Typically, the host would restore CPU registers and stack values and
re-execute the wait or stop instruction.)
1 = Memory access command failed because the CPU entered wait or stop mode.
0 = Memory access did not conflict with a wait or stop instruction.
DVF — Data Valid Failure Status
This status bit is not used in the MC9S08GB/GT because it does not have any slow access memory.
1 = Memory access command failed because CPU was not finished with a slow memory access.
0 = Memory access did not conflict with a slow memory access.
15.5.1.2 BDC Breakpoint Match Register (BDCBKPT)
This 16-bit register holds the address for the hardware breakpoint in the BDC. The BKPTEN and FTS
control bits in BDCSCR are used to enable and configure the breakpoint logic. Dedicated serial BDC
commands (READ_BKPT and WRITE_BKPT) are used to read and write the BDCBKPT register but is
not accessible to user programs because it is not located in the normal memory map of the MCU.
Breakpoints are normally set while the target MCU is in active background mode before running the user
application program. For additional information about setup and use of the hardware breakpoint logic in
the BDC, refer to Section 15.3.4, “BDC Hardware Breakpoint.”
15.5.2 System Background Debug Force Reset Register (SBDFR)
This register contains a single write-only control bit. A serial active background mode command such as
WRITE_BYTE must be used to write to SBDFR. Attempts to write this register from a user program are
ignored. Reads always return $00.
MC9S08GB/GT Data Sheet, Rev. 2.3
Freescale Semiconductor
251