HP 10314D User Manual page 33

HP 103140
prefetch activity. Storage qualification, or the use of storage windows,
can also lead to such occurrences.
The 80386DX has two possible default operand/address sizes, 16 or 32
bits.
This attribute
is
set when a code segment descriptor
is
loaded,
and
is
impoSSiole for the inverse assembler to detect. Therefore, it
must be declared manually by selecting the correct field under the
"Invasm" pop-up. Any instruction with an operand size of 32
bits
(either by default, or by using the operand override prefix) will
be
marked with an"=" symbol in the first column of the 80386DX
mnemonic field to help you distinguish 32-bit operands from 16-bit
operands.
If the inverse assembler seems to be disassembling incorrectly, and the
problem is neither pref etch activity nor storage qualification, it is likely
that the size attnbute
is
set incorrectly.
The 80386DX microprocessor can perform byte, word, and three-byte
transfers, as well as double-word transfers between microprocessor
registers and memory. Byte transfers can occur in any byte on the
32-bit data bus. Word and three-byte transfers can occur across any
contiguous set of bytes that will hold the transfer. The bytes that are
valid in a transfer are indicated by the microprocessor LBEO through
LBE3 lines. The inverse assembler will display "xX' (don't care) for the
bytes of a transfer that are ignored by the microprocessor. In this way
it is possible to determine exactly which bytes were used by the
microprocessor. For example:
:xxxxxxDBH
readmemoiy
(Byte transfer on byte 0)
xx:xx28xxH readmemoiy (Byte transfer on byte 1)
xx:B3xxxxH readmemoiy
(Byte transfer on byte 2)
EOcxxxxxH
readmemoiy (Byte transfer on byte 3)
.xxxx28DBH
readmemoiy (Word transfer on lower word)
.xxB328xxH
readmemoiy (Word transfer on middle word)
ECB3xxxxH
readmemoiy (Word transfer on upper word)
xxB328DBH
readmemoiy
(3-byte transfer on lower three bytes)
ECB328xxH readmemoiy (3-byte transfer on upper three bytes)
ECB328DBH
readmemoiy (Double-word transfer)
80386DX Preprocessor Interface
Analyzing the Intel 80386DX
2-11