User's Manual

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