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8.5 Exception Trap
The exception trap is an interrupt that is requested when the illegal execution of an instruction occurs. In the
NU85E, the illegal opcode exception (ILGOP: Illegal opcode trap) is assigned for the exception trap.
An illegal opcode exception is generated when the sub-opcode of the instruction to be executed next is an illegal
opcode.
8.5.1 Illegal opcode
The illegal opcode, which has a 32-bit long instruction format, is defined as an arbitrary opcode in which bits 10 to
5 are 111111B, bits 26 to 23 are 0111B to 1111B, and bit 16 is 0B.
15
11 10
×
× × × ×
Remark × indicates an arbitrary value.
Caution Since a new instruction may be assigned in the future for the illegal opcode, we recommend that
this opcode not be used.
CHAPTER 8 INTC
Figure 8-14. Illegal Opcode
5 4
1 1 1 1 1 × × × × × × × × × ×
1
Preliminary User's Manual A14874EJ3V0UM
0 31
27 26
23 22
0
1
1
to
1
1
1
17
16
1
× × × × × × 0
1
227
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