MC68030 Datasheet, PDF (409/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
10.4.12 Transfer to/from Top of Stack Primitive
The transfer to/from top of stack primitive transfers an operand between the coprocessor
and the top of the currently active main processor stack (refer to 2.8.1 System Stack). This
primitive applies to general and conditional category instructions. Figure 10-32 shows the
format of the transfer to/from top of stack primitive.
15
14 13 12 11 10
9
8
7
0
CA
PC DR
0
1
1
1
0
LENGTH
Figure 10-32. Transfer To/From Top of Stack Primitive Format
This primitive uses the CA, PC, and DR bits as previously described. If the coprocessor
issues this primitive with CA=0 during a conditional category instruction, the main processor
initiates protocol violation exception processing.
Bits [0-7] of the primitive format specify the length in bytes of the operand to be transferred.
The operand may be one, two, or four bytes in length; other length values cause the main
processor to initiate protocol violation exception processing.
If DR=0, the main processor transfers the operand from the currently active system stack to
the operand CIR. The implied effective address mode used for the transfer is the (A7)+
addressing mode. A one-byte operand causes the stack pointer to be incremented by two
after the transfer to maintain word alignment of the stack.
If DR=1, the main processor transfers the operand from the operand CIR to the currently
active stack. The implied effective address mode used for the transfer is the —(A7)
addressing mode. A one-byte operand causes the stack pointer to be decremented by two
before the transfer to maintain word alignment of the stack.
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MC68030 USER’S MANUAL
10-49