Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
360 Break Module (BRK) MOTOROLA
Break Module (BRK)
21.3 Features
Features of the break module 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
21.4 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 a fter the CPU comple tes 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 21-1 shows the structure of the break
module.