MC68030 Datasheet, PDF (414/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
If DR=1, the main processor reads the number of operands specified in the register select
mask from the operand CIR and writes these operands to the effective address specified in
the instruction using long-word transfers whenever possible. If DR=0, the main processor
reads the number of operands specified in the register select mask from the effective
address and writes them to the operand CIR.
For the control addressing modes, the operands are transferred to or from memory using
ascending addresses. For the postincrement addressing mode, the operands are read from
memory with ascending addresses also, and the address register used is incremented by
the size of an operand after each operand is transferred. The address register used with the
(An)+ addressing mode is incremented by the total number of bytes transferred during the
primitive execution.
For the predecrement addressing mode, the operands are written to memory with
descending addresses, but the bytes within each operand are written to memory with
ascending addresses. As an example, Figure 10-38 shows the format in long-word-oriented
memory for two 12-byte operands transferred from the coprocessor to the effective address
using the —(An) addressing mode. The processor decrements the address register by the
size of an operand before the operand is transferred. It writes the bytes of the operand to
ascending memory addresses. When the transfer is complete, the address register has
been decremented by the total number of bytes transferred. The MC68030 transfers the
data using long-word transfers whenever possible.
31
23
15
7
0
An-2•LENGTH=FINAL An → OP1, BYTE (0)
An-LENGTH → OP0, BYTE (0)
OP1, BYTE (L-1)
INITIAL An →
OP0, BYTE (L-1)
NOTE: OP0, Byte (0) is the first byte written to memory
OP0, Byte (L-1) is the last byte of the first operand written to memory
OP1, Byte (0) is the first byte of the second operand written to memory
OP1, Byte (L-1) is the last byte written to memory
Figure 10-38. Operand Format in Memory for Transfer to —(An)
10-54
MC68030 USER’S MANUAL
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