On a near call, the stack pointer is 2 less than its original value. On a far call, it is 4 less.
The stack pointer value of 07h typically indicates the current position of the stack in memory, often reflecting where the next data will be pushed or popped. In a system using hexadecimal notation, 07h corresponds to the decimal value of 7, which may represent a specific memory offset within the stack segment. This value can change dynamically during program execution as data is pushed to or popped from the stack. Ultimately, the stack pointer's value helps manage the call and return addresses, local variables, and function parameters in a program's execution context.
top pointer of a stack is the pointer that refers to the top most element of the stack.
Both of them are pointers, but otherwise they are completely unrelated. The former points to the current position of the stack, the latter points to the current instruction of the program.
A stack is a data structure in which last item inserted is taken out first . That's why they are known as LIFO (last in first out). Inserting an item in stack is termed as push and taking an item out from stack I s termed as pop. Stack pointer is the pointer that points to the top of the stack or that points the item at the top of the stack and help in adding or deleting the item from the top of stack.
Its main use is to store local variables, arguments and return address each time a function is called.When your program calls a function the following happen :- The function arguments are put on the stack- The current instruction pointer is put on the stack- The program jumps to the start of the function- Space is allocated on the stack to hold local variables- The function executes- The space holding local variables is de-allocated- The instruction pointer is restored and removed from the stack (we are now leaving the function and resuming the calling procedure)- The arguments are removed from the stack
If the stack is empty assume the stack pointer has a value of P. when you push something on the stack you increment P. when you pull something from stack you decrement P.
The stack pointer keeps track of the top of the stack used by the current thread. The program counter keeps track of the next instruction in a program. Both are registers and both store a memory address.
In Intel's 8085 microprocessor, the stack pointer (SP) is decremented by 2 after a POP instruction, as it retrieves a 16-bit value from the stack. In the 8086 microprocessor, the stack pointer is decremented by 2 as well, due to the same reason of retrieving a 16-bit word from the stack. Thus, in both architectures, the stack pointer points to the next available address in the stack after the POP operation.
The execution of the POP instruction typically requires 5 T-states. This includes the time needed for fetching the instruction, reading the stack pointer, accessing the memory location of the data to be popped, updating the stack pointer, and finally storing the data into the specified register or memory location. The exact timing may vary slightly depending on the specific architecture being referenced.
XTHL exchanges HL register with the content of the stack. XTHL followed by RET allows to return to an other address than the one which was previously pushed by a CALL. Eg.: ... CALL FOOBAR ... FOOBAR ... LXI, H @@@@ XTHL RET ;return to @@@@, not after the 'call' Alain FOUERE 22april2009
Program Counter( PC)stores the 16-bit memory address of the next instruction to be fetched. Stack Pointer (SP)stores the address of a memory location which is used as a stack.
SP is the stack pointer and can be used in the stack operations. It cannot be used for fetching the instruction
The PUSH instruction decrements the stack pointer by the size of the operand and then stores its operand at the memory address pointed to by the stack pointer. This leaves the stack pointer always pointing to the last element pushed onto the stack.The POP instruction reverses the sequence, retrieving the operand first, and then incrementing the stack pointer by the size of the operand.Also, PUSH and POP do not work on variables - they only work on register values. You can pop/push a variable, however, by using a register and then storing/retrieving the register to/from memory.
The stack pointer value of 07h typically indicates the current position of the stack in memory, often reflecting where the next data will be pushed or popped. In a system using hexadecimal notation, 07h corresponds to the decimal value of 7, which may represent a specific memory offset within the stack segment. This value can change dynamically during program execution as data is pushed to or popped from the stack. Ultimately, the stack pointer's value helps manage the call and return addresses, local variables, and function parameters in a program's execution context.
Stack pointer points to the topmost / most recently referenced location on the stack; - Nutan
top pointer of a stack is the pointer that refers to the top most element of the stack.
The POP H instruction in the 8085 copies the top of stack to the HL register and then increments the stack pointer by 2. In C pseudo code, the sequence is L = *(SP++); H = *(SP++);