Motorola MC68030 User Manual page 437

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
CA PC DR
I
0
I
1
I
1
I
1
o
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 pro-
cessing.
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 align-
ment of the stack.
MOTOROLA
MC68030 USER'S MANUAL 10-49
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