When a PUSH instruction is executed, the stack pointer (SP) is decremented by 1, and the value of the register specified is written to the memory location pointed to by SP. SP is then decremented by another 1. This example shows the value in H (2F33) being pushed onto the stack, with SP decreasing from 0009 to 0007. A POP instruction pops a value from the stack back into the specified register. This example pops the value 2F back into register B. A subroutine is a segment of code that can be called multiple times from different parts of a program. When a CALL instruction is executed, the return address is pushed onto the stack, and program control

1. MICROPROCESSOR 8085
LECTURE 16
PROGRAMMING EXAMPLE-VII
STACK & SUBROUTINE
PROF. SANDIP DAS

3. STACK
AA
33
2F
0001
0000
0003
0002
0004
0005
0006
0007
0008
0009
2000 LXI SP
0009
SP=0009
2003 LXI H
2F332006 PUSH H
PC=2000
PC=2003
PC=2006
When PUSH instruction is
executed
1. SP will be decremented by
1
2. H will be inserted into the
memory location pointed
by stack pointer
3. Again SP will be
decremented by 1
4. L will be inserted into the
new memory location
pointed by SP
SP=0008
SP=0007
H L
2F 33
EXAMPLE OF PUSH INSTRUCTION

4. STACK
AA
33
2F
0001
0000
0003
0002
0004
0005
0006
0007
0008
0009
2000 LXI SP
0009
SP=0009
2003 LXI H
2F332006 PUSH H
PC=2000
PC=2003
PC=2006
SP=0008
SP=0007
EXAMPLE OF POP INSTRUCTION
2007 POP B PC=2007
B
2F
C
33

5. SUBROUTI
NE
Memory address Mnemonics, operands
2000 LXI SP,20CD H
2003 LXI H,0108 H
2006 MVI B,0F H
2008 CALL 2060 H
200B DCR B
2060 PUSH H
2061 PUSH B
2062 MVI B,05H
2065 POP H
2066 POP B
2067 RET
0F
CB
08
01
STACK
20CD SP=20CD
REGISTE
R
B C H
0F
L
08
2000
2006
2003
2008
2060
2062
2061
2065
MAIN
MEMORY
SUBROUTINE
2066
2067
200B
20CC
20CB
20CA
00 01 080F 05 01