MC908MR16CFUE Datasheet, PDF (251/282 Pages) Freescale Semiconductor, Inc – On-chip programming firmware for use with host personal computer, Clock generator module (CGM)

Chapter 18
Development Support
18.1 Introduction
This section describes the break module, the monitor read-only memory (MON), and the monitor mode
entry methods.
18.2 Break Module (BRK)
The break module (BRK) 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
18.2.1 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 logic 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 microcontroller unit (MCU) to normal operation.
Figure 18-1 shows the structure of the break module.
18.2.1.1 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.
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor
251