Exceptions Because Of Executing Undefined Instructions - Fujitsu F2MC-16LX Hardware Manual

CHAPTER 3 INTERRUPTS
3.7

Exceptions because of Executing Undefined Instructions

When an undefined instruction is executed in the F
exception processing is initiated.
The exception processing is basically the same as the processing for an interrupt.
When an exception within the instructions is detected, the control is transferred from
normal processing to exception processing. Generally, exception processing is a
result of an unpredicted operation. Therefore, use it only for debugging, for software
recovery in an emergency, and similar cases.
■ Occurrence of Exceptions because of Executing Undefined Instructions
2
The F MC-16LX handles all codes not defined in the instruction map as undefined instructions.
When an undefined instruction is executed, the same type of processing as for the software
interrupt instruction, "INT 10", is performed. In other words, after saving the contents of AL, AH,
DPR, DTB, ADB, PCB, PC, and PS to the system stack, the control sets the I flag to "0", sets
the S flag to "1", and then branches to the routine specified by the vector of interrupt number 10.
The PC contents saved to the stack consist of the address where the undefined instruction is
stored. If an undefined code was detected for an instruction code of two or more bytes, the PC
value indicates the address where the undefined code is stored. Therefore, it is possible but
ineffectual to recover the system with an RETI instruction because the same exception will
occur again.
80
2
MC-16LX, an exception occurs and