MC908KX2MDWE Datasheet, PDF (169/210 Pages) Freescale Semiconductor, Inc – High-performance M68HC08 architecture, Fully upward-compatible object code with M6805, M146805, and M68HC05 Families

Chapter 16
Development Support
16.1 Introduction
This section describes the break module, the monitor read-only memory (MON), and the monitor mode
entry methods.
16.2 Break Module (BRK)
The break module can generate a break interrupt that stops normal program flow at a defined address to
enter a background program.
Features include:
• Accessible input/output (I/O) registers during the break interrupt
• Central processor unit (CPU) generated break interrupts
• Software generated break interrupts
• Computer operating properly (COP) disabling during break interrupts
16.2.1 Functional Description
When the internal address bus matches the value written in the break address registers, the break module
issues a breakpoint signal to the CPU. The CPU then loads the instruction register with a software
interrupt instruction (SWI) after completion of the current CPU instruction. The program counter vectors
to $FFFC and $FFFD ($FEFC and $FEFD in monitor mode).
These events can cause a break interrupt to occur:
• A CPU-generated address (the address in the program counter) matches the contents of the break
address registers.
• Software writes a 1 to the BRKA bit in the break status and control register.
When a CPU-generated address matches the contents of the break address registers, the break interrupt
begins after the CPU completes its current instruction. A return-from-interrupt instruction (RTI) in the
break routine ends the break interrupt and returns the MCU to normal operation. Figure 16-1 shows the
structure of the break module.
16.2.1.1 Flag Protection During Break Interrupts
The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear status bits during
the break state.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
Freescale Semiconductor
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