Exception Processing Interrupt - Fujitsu MB90895 Series Hardware Manual

3.5.16

Exception Processing Interrupt

2
The F MC-16LX family performs exception processing when an undefined instruction is
executed.
Exception is basically the same as interrupt. When an exception is detected between
instructions, normal processing is suspended to perform exception processing.
Exception processing is performed when an unexpected operation is performed, and
should be used only for starting recovery software at debugging or in an emergency.
I Exception processing
G
Operation of exception processing
2
The F MC-16LX family treats all instruction codes not defined in the instruction map as undefined
instructions. If an undefined instruction is executed, the processing equal to the software interrupt
instruction "INT # 10" is performed.
At exception processing, the following processing is performed before the transition to interrupt
processing:
• The values of dedicated registers (A, DPR, ADB, DTB, PCB, PC, PS) are saved to the system stack
• The interrupt enable flag (CCR: I) cleared to "0" and interrupts disabled
• The stack flag (CCR: S) set to "1"
The value of the program counter (PC) saved in the stack is a value of the address where undefined
instructions are stored. For instruction codes of 2 bytes or more, the value of the program counter (PC) is a
value of the address where instruction codes that can be identified as undefined are stored. When the type
of exception factor must be determined at exception processing, use the saved program counter (PC).
G
Return from exception processing
When the program counter (PC) indicates an undefined instruction, the interrupt return instruction (RETI)
from exception processing is executed to return to exception processing. Some measures such as
performing a software reset should be taken when returning from exception processing.
CHAPTER 3 CPU
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