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The 80286 microprocessor
can
perform word transfers as well as byte
transfers between microprocessor registers and memory. Furthermore,
byte transfers may occur on either the upper eight bits or the lower
eight bits of the 16-bit data bus. The inverse assembler makes a
distinction between these conditions by displaying
"xx"
(don't care) for
the byte of the transfer that
was
ignored
by
the microprocessor. In this
way, it is possible to determine exactly which byte was used by the
microprocessor:
28B3 memory write
(word transfer)
xxB3
memory write
(byte transfer on lower 8 bits)
28xx
memory write
(byte transfer on uppers bits)
The 80286 instruction set contains four groups of instructions defining
the instruction type in the second opcode, rather than in the first. In
this case, if the second opcode is not stored in analyzer memory, only
the group where an instruction resides
can
be determined. Therefore,
the group name, rather than an instruction mnemonic,
is
displayed in
the mnemonic display field. These group names are defined as follows:
•
Immed - Contains the following instructions when used with
immediate source operands:
ADD
OR
ADC
SBB
AND
SUB
XOR
CMP
•
Shift - Contains the following logical and arithmetic shifts and
rotates:
ROL
ROR
RCL
RCR
SHUSAL
SHR
SAR
Analyzing the Intel 80286
1-19
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