SUBJECT: MICROPROCESSOR AND PERIPHERALS INTERFACING

TOPIC: INSTRUCTION SET AND PROGRAMMING OF 8086

DIFFICULTY: MEDIUM

• The stack is a reserved area of the memory where temporary information may be stored.
• An n-bit stack is used to hold the address of the most recent stack entry. This location which has the most recent entry is called as the top of the stack.
• When the information is written on the stack, the operation is called PUSH.
• When the information is read from the stack, the operation is called POP. The stack works on the principle of Last in First Out or first in Last Out.
• The microprocessor stores the information/data like stacking plates.

Fig below shows stacked plates.

• If we want to remove the first stack plate, then we have to remove all the plates above the first i.e. we have to remove the fourth plate, third plate, second plate and then finally the first plate.
• This indicates that the first plate pushed onto the stack is the last one to be popped from the stack. This operation is called as First In Last Out (FILO).
• The stack is implemented with the help of special memory pointer register called as the stack pointer. The stack pointer’s contents are automatically adjusted to point to the stack.
• The memory location that is currently pointed by the stack pointer is called as top of the stack.
• As shown in the figure the 4th stacked plate represents top of stack.
• When data is to be stored on the stack, the SP increments before storing the data on stack and when the data is to be retrieved/popped from the stack the SP decrements to point next available byte of stored data.
• The stack array can reside anywhere in the on-chip memory.

• In short,

  Stack is used to store information (data) temporarily.

  Stack is a part of memory defined in program by THE USER.

  STACK, the name itself informs about the way data is stored i.e. stack of data.