Transfer From Instruction Stream Primitive - Motorola MC68020 User Manual

The transfer operation word primitive uses the CA and PC bits as described in 7.4.2
Coprocessor Response Primitive General Format. If this primitive is issued with CA = 0
during a conditional category instruction, the main processor initiates protocol violation
exception processing.
When the main processor reads this primitive from the response CIR, it transfers the
F-line operation word of the currently executing coprocessor instruction to the operation
word CIR. The value of the scanPC is not affected by this primitive.

7.4.7 Transfer from Instruction Stream Primitive

The transfer from instruction stream primitive initiates transfers of operands from the
instruction stream to the coprocessor. This primitive applies to general and conditional
category instructions. Figure 7-27 shows the format of the transfer from instruction stream
primitive.
15 14 13
CA PC
Figure 7-27. Transfer from Instruction Stream Primitive Format
The transfer from instruction stream primitive uses the CA and PC bits as described in
7.4.2 Coprocessor Response Primitive General Format. If this primitive is issued with
CA = 0 during a conditional category instruction, the main processor initiates protocol
violation exception processing.
The length field of this primitive specifies the length, in bytes, of the operand to be
transferred from the instruction stream to the coprocessor. The length must be an even
number of bytes. If an odd length is specified, the main processor initiates protocol
violation exception processing (refer to 7.5.2.1 Protocol Violations).
This primitive transfers coprocessor-defined extension words to the coprocessor. When
the main processor reads this primitive from the response CIR, it copies the number of
bytes indicated by the length field from the instruction stream to the operand CIR. The first
word or long word transferred is at the location pointed to by the scanPC when the
primitive is read by the main processor. The scanPC is incremented after each word or
long word is transferred. When execution of the primitive has completed, the scanPC has
been incremented by the total number of bytes transferred and points to the word
following the last word transferred. The main processor transfers the operands from the
instruction stream, using a sequence of long-word writes, to the operand CIR. If the length
field is not an even multiple of four bytes, the last two bytes from the instruction stream are
transferred using a word write to the operand CIR.
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