Stack Operation and Sub Routine [In 8085 Microprocessor]

Definition of Stack in 8085 Microprocessor

Stack is a memory location/block which can be read or written at a single point called as Top of the stack (TOS).

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Stack Operation in 8085  Microprocessor:

A 16-bit register is used for stack operation. It points to the Top of the Stack (TOS). To work with the stack, first of all the address of the stack should be loaded into SP(Stack Pointer).
For example:

• LXI  SP, 16-bit address

There are two operations in stack. They are :

1. PUSH Operation
2. POP  Operation

A. PUSH Operation:

It refers to the insertion of data item into the stack.

Syntax: PUSH RP [RP = Register Pair]

• PUSH B
• PUSH D

For example:

LXI SP, 2099H

MVI H, 42H

MVI L, F2H

PUSH H

B. POP Operation:

It refers to the removal of data item from the stack. 

Syntax: POP RP

• POP B
• POP D

Sub Routine in 8085 Microprocessor

So what is a Sub Routine ? | Definition of Sub Routine

A Sub Routine is a group of instructions to perform arithmetic and other time delay operation. 

• Subroutine resides in the memory block as separate unit from main program. A Sub routine in assembly language is similar to equivalent to the function in high level language.
• Call of sub routine requires to transfer program counter to first address of sub routine. 
• During this control transfer calling program need to be saved in stack. 
• Last statement of any sub routine is Return statement. The execution of return statement transfer control to next instruction of calling program by reloading PC(Program Counter) with previously stored values.
• The use of sub routine increases overhead in program but often prefer by programmers for modularity.
• In 8085, CALL and RET are instructions for sub routine.

Conditional Call Instructions
Mnemonics	Description
CC 16-bit address	Call Sub Routine on Carry(CF=1)
CNC 16-bit address	Call Sub Routine on No Carry(CF=0)
CZ 16-bit address	Call on Zero(Z=1)
CNZ 16-bit address	Call on No Zero(Z=0)
CM 16-bit address	Call on Minus(SF=1)
CP 16-bit address	Call on Plus(SF=0)
CPE 16-bit address	Call on Even Parity(P=1)
CPO 16-bit address	Call on Odd Parity(P=0)
Conditional Return Instructions
RC	Return on Carry
RNC	Return on No Carry
RZ	Return on Zero
RNZ	Return on No Zero
RM	Return on Minus
RP	Return on Plus
RPE	Return on Even Parity
RPO	Return on Odd Parity

Related Posts: 

• 8085 Microprocessor Features, Pin Diagram, Architecture
• 8086 Microprocessor Features, Architecture
• All 8085 Instructions with Operand, Size, Addressing Mode, Machine Cycle, T-States
• Timing Diagram [8085 Microprocessor]