PUSH and POP Instructions

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The PUSH instruction first decrements ESP and then copies either a 16- or 32- bit source operand into the stack. A 16-bit operand causes ESP to be decremented by 2. A 32-bit operand causes ESP to be decremented by 4.

PUSH — Push Word(s) onto Stack
Usage: PUSH src Flag O D I S Z A P C Result                 Decrements ESP by the size of the operand (two or four, byte values are sign extended) and transfers one or two words from source to the stack top. Clocks Operands 286 386 486 Size Bytes reg16 3 2 1 1 reg32   2 1 1 mem16 5 5 4 2-4 mem32   5 4 2-4 segreg 3 2 3 1 immed 3 2 1 2-3

The POP instruction removes a value from the stack and places it in a register or variable. After the value is popped from the stack, the stack pointer is incremented to point to the next-highest location in the stack.

POP — Push Word(s) off Stack
Usage: POP dest Flag O D I S Z A P C Result                 Transfers word(s) at the current stack top pointed by ESP to the destination then increments ESP to point to the new stack top. Clocks Operands 286 386 486 Size Bytes reg16 5 4 4 1 reg32     4 1 mem16 5 5 6 2-4 mem32     6 2-4 segreg 5 7 3 1