Module 4.1 Logical Instructions

AND
OR
XOR
TEST
NOT

Five primary bitwise logical instructions that are used to manipulate, test, set, or clear individual bits within registers or memory locations.

Two-operand instructions: INSTRUCTION operand1, operand2
Single-operand instruction: NOT operand1

Syntax Pattern

The first operand can be a register or memory location. The second operand can be a register, memory, or immediate value. Operations directly between two memory locations are not supported.

Rule

These operations update CPU flags, including CF (Carry), OF (Overflow), PF (Parity), SF (Sign), and ZF (Zero).

Flags Affected

AND Instruction

It clears specific bits (masking) or testing bit conditions. Performs a bitwise AND operation (returns 1 only if both corresponding bits are 1).

OR Instruction

Setting specific bits to 1. Performs a bitwise OR operation (returns 1 if at least one corresponding bit is 1).

XOR Instruction

Toggling bits or efficiently clearing registers to zero. Performs a bitwise Exclusive-OR operation (returns 1 if corresponding bits are different, 0 if identical).

TEST Instruction

Checking values or bit states without altering data. Performs a non-destructive bitwise AND operation. It updates CPU flags (e.g., ZF) without modifying the destination operand.

NOT Instruction

Performs a bitwise NOT (one's complement), inverting all bits of the operand (0 becomes 1, 1 becomes 0).