Stack in 8051

Stack in 8051

RAM locations from 08H to 1FH can be used as stack. Stack is used to store the data temporarily.

Stack is last in first out (LIFO)

Stack pointer (SP) →

8bit register

It indicate current RAM address available for stack or it points the top of stack.

Initially by default at 07H because first location of stack is 08H.

After each PUSH instruction the SP is incremented by one while in MC after PUSH instruction SP is decremented.

After each POP instruction the SP is decremented

Example:

MOV R6,#25H;

MOV R1,#12H;

MOV R4,#OF3H;

PUSH 06H;

PUSH 01H; POP 04H;

if we want to use more than 24byte (08H to 1FH) of stack. We can change SP to point RAM address 30H to 7FH by MOV SP,

Conflicting of Register Banks and Stack

We know locations from 08H to 1FH is used as stack and it is also used as register bank.

If in the program, we use the Register Bank 1 to 3 and also use the stack then conflicts exist and error can be possible.

For removing this situation we use the stack from location 30H to 7FH by shifting SP to 2FH.

MOV SP,#2FH;

DPTR Data Pointer in 8051

16 bit register, it is divided into two parts DPH and DPL.

DPH for Higher order 8 bits, DPL for lower order 8 bits.

DPTR, DPH, DPL these all are SFRs in 8051.

Special Function Register

RAM scratch pad, there is extra 128 byte RAM which is used to store the SFRs

Following figure shows special function bit address, all access to the four I/O ports CPU register, interrupt control register, timer/counter, UART, power control are performed through registers between 80H and FFH.