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C-31
INSTRUCTION SET DESCRIPTIONS
NEG Negate:
NEG
dest
Subtracts the destination operand,
which may be a byte or a word, from 0
and returns the result to the desti-
nation. This forms the two's
complement of the number, effectively
reversing the sign of an integer. If the
operand is zero, its sign is not
changed. Attempting to negate a byte
containing –128 or a word containing –
32,768 causes no change to the
operand and sets OF.
Instruction Operands:
NEG reg
NEG mem
When Source Operand is a Byte:
(dest) ← FFH – (dest)
(dest) ← (dest) + 1 (affecting flags)
When Source Operand is a Word:
(dest) ← FFFFH – (dest)
(dest) ← (dest) + 1 (affecting flags)
AF
CF
DF –
IF –
OF
PF
SF
TF –
ZF
NOP No Operation:
NOP
Causes the CPU to do nothing.
Instruction Operands:
none
None AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
NOT Logical Not:
NOT
dest
Inverts the bits (forms the one's
complement) of the byte or word
operand.
Instruction Operands:
NOT reg
NOT mem
When Source Operand is a Byte:
(dest) ← FFH – (dest)
When Source Operand is a Word:
(dest) ← FFFFH – (dest)
AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
Table C-4. Instruction Set (Continued)
Name Description Operation
Flags
Affected
NOTE: The three symbols used in the Flags Affected column are defined as follows:
– the contents of the flag remain unchanged after the instruction is executed
? the contents of the flag is undefined after the instruction is executed
the flag is updated after the instruction is executed