MC68030 Datasheet, PDF (406/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
10.4.10 Write to Previously Evaluated Effective Address Primitive
The write to previously evaluated effective address primitive transfers an operand from the
coprocessor to a previously evaluated effective address. This primitive applies to general
category instructions. If the coprocessor uses this primitive during the execution of a
conditional category instruction, the main processor initiates protocol violation exception
processing. Figure 10-30 shows the format of the write to previously evaluated effective
address primitive.
15
14 13 12 11 10
9
8
7
0
CA
PC
1
0
0
0
0
0
LENGTH
Figure 10-30. Write to Previously Evaluated EffectiveAddress Primitive Format
This primitive uses the CA and PC bits as previously described.
Bits [0-7] of the primitive format specify the length of the operand in bytes. The MC68030
transfers operands between zero and 255 bytes in length.
When the main processor receives this primitive during the execution of a general category
instruction, it transfers an operand from the operand CIR to an effective address specified
by a temporary register within the MC68030. When a previous primitive for the current
instruction has evaluated the effective address, this temporary register contains the
evaluated effective address. Primitives that store an evaluated effective address in a
temporary register of the main processor are the evaluate and transfer effective address,
evaluate effective address and transfer data, and transfer multiple coprocessor registers
primitive. If this primitive is used during an instruction in which the effective address
specified in the instruction operation word has not been calculated, the effective address
used for the write is undefined. Also, if the previously evaluated effective address was
register direct, the address written to in response to this primitive is undefined.
The function code value during the write operation indicates either supervisor or user data
space, depending on the value of the S bit in the MC68030 status register when the
processor reads this primitive. While a coprocessor should request writes to only alterable
effective addressing modes, the MC68030 does not check the type of effective address
used with this primitive. For example, if the previously evaluated effective address was
program counter relative and the MC68030 is at the user privilege level (S=0 in status
register), the MC68030 writes to user data space at the previously calculated program
relative address (the 32-bit value in the temporary internal register of the processor).
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MC68030 USER’S MANUAL
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