Stack and its usage in assembly language

2. Stacks
Usman Bin Saad FA14-BSE-4C-118
Shahid Iqbal FA14-BSE-4C-160
Haseeb Ahmad FA14-BSE-4C-129
Submitted to
Miss Arubah

3. Stack
• A stack is a data structure that stores data in such a way that the
last piece of data stored, is the first one retrieved i.e. Last in,
First out LIFO / First in Last out FILO
• Only access to the stack is the top element
• Anything added to the stack goes on the “top” of the stack
• Anything removed from the stack is taken from the “top” of the
stack
• Things are removed in the reverse order from that in which they
were inserted

5. Basic Stack Operations
• There are three Basic Stack Operations which are discussed below
• Push
• Pop
• Stack Top

6. Push
• The operation to place a new item at the top of the stack

7. Pop
• The operation to remove the next item from the top of the stack

9. Implementing a Stack
• At least three different ways to implement a stack
• array
• vector
• linked list

10. Stack in Assembly Language
• The stack segment register holds the starting address of the stack segment
in the memory. Majorly SS is used for the following purposes namely:
1.To hold the temporary results.
2.To hold the return address of the subroutine.
3.Finally to handle the interrupts
• SS (Stack Segment) Register: holds stack Segment Address
• SP (Stack Pointer) Register: initialized to the value specified with the .STACK
directive, represents empty stack position
• When stack is not empty, SP represents the top of the Stack

11. Stack (cont ..)
• In order to save the contents of a register during the execution, so that it
can be used later for purposes.
• To do so, the microprocessor has a area of memory where the contents of
specified registers or memory location can be saved temporarily, and is
called STACK.
• It is a top-down data structure whose elements are accessed using the
pointer that is implemented using the SP and SS registers.
• As we go on storing the data words onto the stack, the pointer goes on
decrementing.

12. PUSH And PUSHF
• PUSH: Used to add a new source (16-bit register or memory word) on stack
Syntax:
PUSH source
• Execution of PUSH causes:
SP is decreased by 2
A copy of source contents is moved to the address specified by SS:SP.
Source remains unchanged
• PUSHF has no operand and it pushes the contents of FLAG register onto
the stack.
• Usually this is done whenever the processor is interrupted
Syntax: PUSHF

14. POP And POPF
• POP: Used to remove top item from stack to destination (i.e. a 16-bit register
or memory word).
Syntax:
POP destination
• Execution of POP causes:
The contents of SS:SP (top of the stack) is moved to the destination.
SP is increased by 2
• POPF has no operand and pops the top of the stack into FLAG register.
• SP is incremented by 2 after executing this instant.
Syntax: POPF