7/28/2019 Zero Address Instructions

1/3

Zero Address Instructions

An instruction that contains no address fields; operand sources and destination are both implicit. It

may for example enable stack processing: a zero-address instruction implies that the absolute address

of the operand is held in a special register that is automatically incremented (or decremented) to point

to the location of the top of the stack.

Example: ADD

The above instruction consists of an operation code only. It has no addrss field. The operation has

the effect of popping the two top numbers from the stack, adding the numbers and pushing the sum

into the stack. Here all operands are performed within stack. To evaluate arithmetic expressions, they

must be first converted into reverse polish notation. The operand at address X is pushed on to the top

of the stack. Automatically the stack pointer is incremented.

Example:

X=(A + B) + (C + D)

PUSH A ; TOS

7/28/2019 Zero Address Instructions

2/3

M[X] = Memory operand at address X.

Example:

X=(A + B)X(C + D)

LOAD A ; AC

7/28/2019 Zero Address Instructions

3/3

Example:

X=(A + B)-(C + D)

MOV R1,A ; R1