Slide 11.3: Conditional jumps (cont.) Slide 11.5: AND instruction Home

Boolean Instructions

---

Boolean logic is important in circuitry design and has a parallel in programming logic. The instructions for boolean logic are AND, OR, XOR, TEST, and NOT, all of which can be used to clear, set, and test bits. The following table shows selected boolean instructions.

Operation	Description
AND	The Boolean function which is true only if all its arguments are true.
OR	The Boolean function which is true if any of its arguments are true.
XOR	Exclusive or. “A XOR B” means “A or B, but not both.”
NOT	The Boolean function which is true only if its input is false.
TEST	TEST sets the flags as AND does, but does not change the bits referenced in the target operand.

AND Instruction
The AND instruction performs a boolean (bitwise) AND operation between each pair of matching bits in two operands and places the result in the destination operand.

AND — Logical AND
Usage: AND dest, src Flag O D I S Z A P C Result ?     * * ? * ? Performs a logical AND of the two operands replacing the destination with the result. Clocks Operands 286 386 486 Size Bytes reg, reg 2 2 1 2 mem, reg 7 7 3 2-4 reg, mem 7 6 1 2-4 reg, immed 3 2 1 3-4 mem, immed 7 7 3 3-6 accum, immed 3 2 1 2-3

^†The AND instruction is often used to clear selected bits and preserve others.