mc68hc908ap8a Freescale Semiconductor, Inc, mc68hc908ap8a Datasheet - Page 290

• Manufacturer Part Number: mc68hc908ap8a
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Break Module (BRK)
The following events can cause a break interrupt to occur:
When a CPU-generated address matches the contents of the break address registers, the break interrupt
is generated. A return-from-interrupt instruction (RTI) in the break routine ends the break interrupt and
returns the MCU to normal operation.
21.3.1 Flag Protection During Break Interrupts
The system integration module (SIM) controls whether or not module status bits can be cleared during
the break state. The BCFE bit in the break flag control register (BFCR) enables software to clear status
bits during the break state.
21.3.2 CPU During Break Interrupts
When the internal address bus matches the value written in the break address registers or when software
writes a 1 to the BRKA bit in the break status and control register, the CPU starts a break interrupt by:
The break interrupt timing is:
By updating a break address and clearing the BRKA bit in a break interrupt routine, a break interrupt can
be generated continuously.
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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.
Loading the instruction register with the SWI instruction
Loading the program counter with $FFFC and $FFFD ($FEFC and $FEFD in monitor mode)
When a break address is placed at the address of the instruction opcode, the instruction is not
executed until after completion of the break interrupt routine.
When a break address is placed at an address of an instruction operand, the instruction is
executed before the break interrupt.
When software writes a 1 to the BRKA bit, the break interrupt occurs just before the next instruction
is executed.
IAB15–IAB0
Figure 21-2. Break Module Block Diagram
IAB15–IAB8
IAB7–IAB0
MC68HC908AP A-Family Data Sheet, Rev. 3
BREAK ADDRESS REGISTER HIGH
BREAK ADDRESS REGISTER LOW
Figure 21-2
8-BIT COMPARATOR
8-BIT COMPARATOR
shows the structure of the break module.
CONTROL
BREAK
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