Motorola USB08 Betriebsanleitung PDF herunterladen (Seite 17)

5 DEBUGGING

5.1 Breakpoints

Tracing, and running programs to breakpoints, requires that breakpoints can be established at the right

places in the MCU program code. On the HC908 chips only a single breakpoint can be set at one time,

by writing a value to the breakpoint register. Programs may be run or traced in both RAM and FLASH

memory. When tracing at a branch instruction, Xplor8 calculates where program execution will

continue by its own analysis of the condition code register, and sets the next breakpoint accordingly.

A breakpoint cannot be set at:

• illegal opcodes

• indexed jump instructions

• the SWI instruction

• BIH or BIL instructions

• any instruction which jumps or branches to itself

A breakpoint may be set or deleted as part of the Go (Run) command. The Trace command

automatically sets the breakpoint. When a breakpoint address has been written, the Breakpoint

The breakpoint module in the HC908xx MCU's has some quirks, probably due to the instruction

pre-fetch architecture. You may find that setting breakpoints at branch destinations or at RTS

instructions results in a running program stopping at unexpected places. This odd behavior does not

appear to affect tracing. The \Samples\ subdirectory contains a program which demonstrates this.

5.2 SWI in user code

If a Software Interrupt (SWI) instruction is encountered by a running program, while in monitor mode,

control will return to the monitor and this is useful for testing code segments. When control does

return to the monitor in these circumstances, the output window will display the message: ‘unexpected

break received’.

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Motorola USB08 Betriebsanleitung Seite 17