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MC9S08LL64 MCU Series Reference Manual, Rev. 5
Freescale Semiconductor
369
19.3.1.2
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
4
FTS
Force/Tag Select — When FTS = 1, a breakpoint is requested whenever the CPU address bus matches the
BDCBKPT match register. When FTS = 0, a match between the CPU address bus and the BDCBKPT register
causes the fetched opcode to be tagged. If this tagged opcode ever reaches the end of the instruction queue,
the CPU enters active background mode rather than executing the tagged opcode.
0 Tag opcode at breakpoint address and enter active background mode if CPU attempts to execute that
instruction
1 Breakpoint match forces active background mode at next instruction boundary (address need not be an
opcode)
3
CLKSW
Select Source for BDC Communications Clock — CLKSW defaults to 0, which selects the alternate BDC clock
source.
0 Alternate BDC clock source
1 MCU bus clock
2
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.
0 Target CPU is running user application code or in active background mode (was not in wait or stop mode when
background became active)
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
1
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.)
0 Memory access did not conflict with a wait or stop instruction
1 Memory access command failed because the CPU entered wait or stop mode
0
DVF
Data Valid Failure Status — This status bit is not used in the MC9S08LL64 Series because it does not have
any slow access memory.
0 Memory access did not conflict with a slow memory access
1 Memory access command failed because CPU was not finished with a slow memory access
Table 19-2. BDCSCR Register Field Descriptions (continued)
Field
Description