FMA Unit 2.3 Stack and its Operations

Stack and its Operations

Stack in the 8051

The stack is a section of a RAM used by the CPU to store information such as data or memory address on temporary basis. And which work on LIFO (Last in and first out) basis. The CPU needs this storage area considering limited number of registers.

As the stack is a section of a RAM, there are registers inside the CPU to point to it. The register used to access the stack is known as the stack pointer register.

The storing operation of a CPU register in the stack is known as a PUSH, and getting the contents from the stack back into a CPU register is called a POP.

Pushing into the Stack

In the 8051, the stack pointer (SP) points to the last used location of the stack. When data is pushed onto the stack, the stack pointer (SP) is incremented by 1. When PUSH is executed, the contents of the register are saved on the stack and SP is incremented by 1. To push the registers onto the stack, we must use their RAM addresses.

Popping from the Stack

Popping the contents of the stack back into a given register is the opposite to the process of pushing. With every pop operation, the top byte of the stack is copied to the register specified by the instruction and the stack pointer is decremented once.