Stack in 8085 microprocessor

1. D R . R . H E P ZI P R A M I L A D E VA M A N I ,
A S S I S TA N T P R O F E S S O R O F P H Y S I C S ,
V. V. VA N N I A P E RU M A L C O L L E G E F O R W O M E N ,
V I R U D H U N A G A R .
STACK IN 8085 MICROPROCESSOR

2. STACK
 The stack is a group of memory locations in the RAM
(R/W) memory that is used for temporary storage of
binary information during the execution of the
program.
 The last memory location of the occupied portion of
the stack is called stacktop.
 The starting memory location of the stack is defined
in the main program by using LXI or SPHL
instruction.

3. STACK
 Data are stored in the
stack on last-in-first-out
(LIFO) principle and
data are retrieved from
the stack first-in-last-out
principle.
 Figure shows typical
stack and stack top
location.

4. INSTRUCTIONS
 PUSH instruction is used to store data in stack
 POP instruction is to retrieve the contents
 A register pair is always specified along with these
PUSH and POP instructions.
PUSH B POP B
PUSH D POP D
PUSH H POP H
PUSH PSW POP PSW
B,D,H PSW specifies register pairs BC, DE, HL, A and
Flags

5. PUSH INSTRUCTION
 PUSH Rp
 PUSH instruction can be explained with an example
LXI SP,2605H
LXI B, 2550H
PUSH B
Delay Counter
POP B

6. PUSH Instruction
 Step 1: LXI SP, 2605 will initialize SP register 2605
 Step 2: LXI B, 2550H will initialize or load BC register
pair with 2550H data so B = 25 and C = 50.
 Step 3: The execution of PUSH b instruction will be
 The stack pointer is decreased by one to 2604H and the
contents of the B register are copied to memory location
2604H.
 The stack pointer is again decreased by one to 2603H and
the contents of the C register are copied to memory
location 2603H.
 The contents of the register pair BC are not destroyed.
However , BC is made available for the delay counter.
 The execution of PUSH operation is shown in Figure.

7. PUSH OPERATION

8. POP INSTRUCTION
 After the delay count, the instruction POP B restores the
original contents of the register pair BC.
 The execution of POP B instruction will be
 The contents of the top of the stack location shown by the
stack pointer are copied in the C register and the stack pointer
is increased by one to 2604H
[C]  [SP], [SP]  [SP] + 1
 The contents of the top of the stack are copied in the B
register and the stack pointer is increased by one
[B]  [SP], [SP]  [SP] + 1
 The contents of the memory locations 2603H and2604H are
not destroyed until some other data bytes are stored in these
locations.
 The execution of POP operation is shown in Figure.

9. POP OPERATION

10. REFERENCE
 Microprocessor , Microcomputer ,
Microcontroller and interfacing- M.K
Gupta,Paragon International Publishers, 2nd
Edition(2007).