Intel 80286, 80287 Division Instructions, Logical Instructions, Boolean Operation Instructions

BASIC INSTRUCTION SET

3.3.4 Division Instructions

DIV (Unsigned Integer Divide) performs an unsigned division of the accumulator by the source operand. If the source operand is a byte, it is divided into the double-length dividend assumed to be in registers AL and AH (AH = most significant byte; AL = least significant byte). The single-length quotient is returned in AL, and the single-length remainder is returned in AH.

If the source operand is a word, it is divided into the double-length dividend in registers AX and DX. The single-length quotient is returned in AX, and the single-length remainder is returned in DX. Non- integral quotients are truncated to integers toward O. The remainder is always less than the quotient.

For unsigned byte division, the largest quotient is 255. For unsigned word division, the largest quotient is 65,535. DIY leaves OF, SF, ZF, AF, PF, and CF undefined. Interrupt (INT 0) occurs if the divisor is zero or if the quotient is too large for AL or AX.

Example: DIY BX. Replaces the contents of AX with the unsigned quotient of the doubleword value contained in DX and AX, divided by BX. The unsigned modulo replaces the contents of

DX.

Example: DIY BL. Replaces the contents of AL with the unsigned quotient of the word value in AX, divided by BL. The unsigned modulo replaces the contents of AH.

IDIV (Signed Integer Divide) performs a signed division of the accumulator by the source operand. IDlY uses the same registers as the DIY instruction.

For signed byte division, the maximum positive quotient is +127 and the minimum negative quotient is -128. For signed word division, the maximum positive quotient.is +32,767 and the minimum negative quotient is - 32,768. Non-integral results are truncated towards O. The remainder will always have the same sign as the dividend and will be less than the divisor in magnitude. IDlY leaves OF, SF, ZF, AF, PF, and CF undefined. A division by zero causes an interrupt (INT 0) to occur if the divisor is 0 or if the quotient is too large for AL or AX.

Example: IDlY WORDOPRND. Replaces the contents of AX with the signed quotient of the double- word value contained in DX and AX, divided by the value contained in the memory word labeled WORDOPRND. The signed modulo replaces the contents of DX.

3.4LOGICAL INSTRUCTIONS

The group of logical instructions includes the Boolean operation instructions, rotate and shift instruc- tions, type conversion instructions, and the no-operation (NOP)instruction.

3.4.1 Boolean Operation Instructions

Except for the NOT and NEG instructions, the Boolean operation instructions can use two register operands, a general purpose register operand with a memory operand, an immediate operand with a general purpose register operand, or a memory operand. The NOT and NEG instructions are unary operations that use a single operand in a register or memory.

AND (And) performs the logical "and" of the operands (byte or word) and returns the result to the destination operand. AND clears OF and DF, leaves AF undefined, and updates SF, ZF, and PF.

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