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HIGH
ADDRESS
LOW
ADDRESS
BASIC INSTRUCTION SET
h
BEFORE
PUSHA
AFTER
PUSHA
SS
LIMIT
SP
SS
PUSHA
copies
Ihe
conlenls
of
Ihe
elghl
general reglslers
10
Ihe
slack
In Ihe above order. The Inslrucllon decremenls
SP
by
16
bytes
(8 words)
10
polnllo
Ihe
l.sl
word pushed on Ihe
slack.
G30108
Figure 3-2. PUSHA
POP
(Pop)
transfers the word at the current top of stack (indicated by SP) to the destination operand,
and then increments
SP
by two to point to the
new
top of stack. See figure
3-3.
POP moves information
from the stack to either a register or memory. The only restriction
on
POP
is
that
it
cannot place a
value
in
register CS.
Example:
POP BX. Replaces the contents of register
BX
with the contents of the memory location
at the top of stack.
paPA
(Pop
All
Registers) restores the registers saved
on
the stack
by
PUSHA, except that
it
ignores
the value of SP. See figure
3-4.
Example:
papA.
Pops from the stack the saved contents of the general registers, and restores the
registers (except SP)
to
their original state.
3-3