CPU16
REFERENCE MANUAL
DEVELOPMENT SUPPORT
MOTOROLA
10-5
10.1.4 Combining Opcode Tracking with Other Capabilities
Pipeline state signals are useful during normal instruction execution and execution of
exception handlers. Refer to
SECTION 9 EXCEPTION PROCESSING
for a detailed
discussion of exceptions and exception handlers. The signals provide a complete
model of the pipeline up to the point a breakpoint is acknowledged.
Breakpoints are acknowledged after an instruction has executed, when it is in pipeline
stage C. A breakpoint can initiate either exception processing or background debug-
ging mode. See
10.2 Breakpoints10.2 Breakpoints
and
10.3 Opcode Tracking and
Breakpoints10.3 Opcode Tracking and Breakpoints
for more information. IPIPE0/
IPIPE1 are not usable when the CPU16 is in background debugging mode. Complete
information is contained in
10.4 Background Debug Mode (BDM)
.
10.1.5 CPU16 Instruction Pipeline State Signal Flow
Figure 10-3
is the flow diagram required to properly interpret instruction pipeline state
signals.
10.2 Breakpoints
Breakpoints are set by internal assertion of the IMB BKPT signal or by external asser-
tion of the microcontroller BKPT pin. The CPU16 supports breakpoints on any memory
access. Acknowledged breakpoints can initiate either exception processing or back-
ground debugging mode. After BDM has been enabled, the CPU16 will enter BDM
when either BKPT input is asserted.
If BKPT assertion is synchronized with an instruction prefetch, the instruction is
“tagged” with the breakpoint when it enters the pipeline, and the breakpoint occurs af-
ter the instruction executes.
If BKPT assertion is synchronized with an operand fetch, breakpoint processing oc-
curs at the end of the instruction during which BKPT is latched.
Breakpoints on instructions that are flushed from the pipeline before execution are not
acknowledged, but operand breakpoints are always acknowledged. There is no break-
point acknowledge bus cycle when BDM is entered. See
SECTION 9 EXCEPTION
PROCESSING
for complete information about breakpoint exceptions.
F
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.