Freescale Semiconductor MC68881 - MC68881 Register-To-Register Instruction Dialog; MC68881;MC68882 External-To-Register Instruction Dialog

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MC68020/MC68030 I
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Indicates an optional operation. The MC68881
allows the "Pass PC" operation to be performed at
the discretion of the main processor without causing
a protocol violation (the MC68020/MC68030 always
passes the PC when it is requested). However, the
MC68882 requires the "Pass PC'" operation to be
performed when requested. Some operand transfer
bus transactions ere optional, based on the size and
location of source or destination operands external to
the MC68881/MC68BS2.
Indicates an operation that is performed only for
certain cases of the instruction or operation being
executed. These operations are identified explicitly in
the diagrams as to the conditions under which they
are executed.
Indicates the encoding of the Response CIR at points
in an instruCtion dialog where it will normally not be
read by the MC68020/MC68030. This information is
included tot designers of systems that do not utilize
the MC68020/MC68030 as the main processor.
When an encoding is indicated for the Response CIR,
it is not changed until a new encoding is given.
Figure 7-17. MC68881 Register-to-Register Instruction Dialog
thus avoiding spurious request primitives in non-MPU based systems. The MC68881 dialog
for this instruction type, which also applies to the MC68882 with operand data formats
other than single, double, or extended, is shown in Figure 7-18.
When the operand data format is single, double, or extended, the MC68882 issues the
evaluate <ea> and transfer data primitive with CA=0 instead of CA= 1. Figure 7-19 shows
the dialog for the MC68882 external-to-register instructions with single, double, or extended
data format operands.
If any arithmetic exceptions are enabled, the FPCP requests the transfer of the program
counter with the first primitive. However, the main processor using an MC68881 can ignore
this request; the MC68882 issues a protocol violation if the main processor ignores the
request.
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Figure 7-18. MC68881/MC68882 External-to-Register Instruction Dialog
MC68881/MC68882 USER'S MANUAL FREESCALE
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