MC68030 Datasheet, PDF (264/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Exception Processing
An illegal instruction exception is also taken if a breakpoint acknowledge bus cycle (see
7.4.2 Breakpoint Acknowledge Cycle) is terminated with the assertion of the bus error
signal. This implies that the external circuitry did not supply an instruction word to replace
the BKPT instruction word in the instruction pipe.
Instruction word patterns with bits [15:12] equal to $A are referred to as unimplemented
instructions with A-line opcodes. When the processor attempts to execute an
unimplemented instruction with an A-line opcode, an exception is generated with vector
number 10, permitting efficient emulation of unimplemented instructions.
Instructions that have word patterns with bits [15:12] equal to $F, bits [11:9] equal to $0, and
defined word patterns for subsequent words are legal MMU instructions. Instructions that
have bits [15:12] of the first words equal to $F, bits [11:9] equal to $0, and undefined patterns
in subsequent words are treated as unimplemented instructions with F-line opcodes when
execution is attempted in supervisor mode. When execution of the same instruction is
attempted in user mode, a privilege violation exception is taken. The exception vector
number for an unimplemented instruction with an F-line opcode is number 11.
The word patterns with bits [15:12] equal to $F and bits [11:9] not equal to zero are used for
coprocessor instructions. When the processor identifies a coprocessor instruction, it runs a
bus cycle referencing CPU space type $2 (refer to 4.2 Address Space Types) and
addressing one of seven coprocessors (1-7, according to bits [11:9]). If the addressed
coprocessor is not included in the system and the cycle terminates with the assertion of the
bus error signal, the instruction takes an unimplemented instruction (F-line opcode)
exception. The system can emulate the functions of the coprocessor with an F-line
exception handler. Refer to Section 10 Coprocessor Interface Description for more
details.
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MC68030 USER’S MANUAL
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