MC68030 Datasheet, PDF (423/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
The coprocessor can signal a protocol violation to the main processor with the take mid-
instruction exception primitive. To maintain consistency, the vector number should be 13, as
it is for a protocol violation detected by the main processor. When the main processor reads
this primitive, it proceeds as described in 10.4.19 Take Mid-Instruction Exception
Primitive. If the exception handler does not modify the stack frame, the MC68030 returns
from the exception handler and reads the response CIR.
10.5.1.2 COPROCESSOR-DETECTED ILLEGAL COMMAND OR CONDITION WORDS.
Illegal coprocessor command or condition words are values written to the command CIR or
condition CIR that the coprocessor does not recognize. If a value written to either of these
registers is not valid, the coprocessor should return the take pre-instruction exception
primitive in the response CIR. When it receives this primitive, the main processor takes a
pre-instruction exception as described in 10.4.18 Take Pre-Instruction Exception
Primitive. If the exception handler does not modify the main processor stack frame, an RTE
instruction causes the MC68030 to reinitiate the instruction that took the exception. The
coprocessor designer should ensure that the state of the coprocessor is not irrecoverably
altered by an illegal command or condition exception if the system supports emulation of the
unrecognized command or condition word.
All Motorola M68000 coprocessors signal illegal command and condition words by returning
the take pre-instruction exception primitive with the F-line emulator exception vector number
11.
10.5.1.3 COPROCESSOR DATA-PROCESSING EXCEPTIONS. Exceptions related to the
internal operation of a coprocessor are classified as data-processing-related exceptions.
These exceptions are analogous to the divide-by-zero exception defined by M68000
microprocessors and should be signaled to the main processor using one of the three take
exception primitives containing an appropriate exception vector number. Which of these
three primitives is used to signal the exception is usually determined by the point in the
instruction operation where the main processor should continue the program flow after
exception processing. Refer to 110.4.18 Take Pre-Instruction Exception Primitive,
10.4.19 Take Mid-Instruction Exception Primitive, and 10.4.20 Take Post-Instruction
Exception Primitive.
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MC68030 USER’S MANUAL
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