Chapter 7Logic, Shift and Rotate Instructions (Part 1)PREPARED BY

AHMED AL MAROUF

LECTURER, CSE, DAFFODIL INTERNATIONAL UNIVERSITY (DIU)

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OutlinePart 1 contains only

Logic Instructions AND

OR

XOR

NOT

Applications of Logic Instructions CLEAR

SET

COMPLEMENT /CHANGE

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Logic Instructions Logic instructions has the ability to manipulate individual bits.

The binary values of 0 and 1 are treated as False and True, respectively.

Logic Operations for 8086 assembly language are: AND

OR

XOR and

NOT

When logic operation is applied to 8-bit or 16-bit operands, the result is obtained by applying the logic operation at each bit position.

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Truth Table of Logic OperationsOperands Logic Operations

Operand 1 Operand 2 AND OR XOR NOT Op1

0 0 0 0 0 1

0 1 0 1 1 1

1 0 0 1 1 0

1 1 1 1 0 0

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Examples

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Assembly Instructions

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Effect on Flags of Logic Instructions

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Applications of Logic Instructions

1. Clearing bits

2. Setting bits

3. Complementing bits

These operations can be performed on individual bits.

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Clearing bits Clearing means changing the bits as follow:

0 to 0

1 to 0

Therefore,

Masks for

Changed – 0

Unchanged - 1

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Operands Logic Operations

Original Bit Mask AND

0 0 0

0 1 0

1 0 0

1 1 1

Setting bits Setting means changing the bits as follow:

0 to 1

1 to 1

Therefore,

Masks for

Changed – 1

Unchanged - 0

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Operands Logic Operations

Original Bit Mask OR

0 0 0

0 1 1

1 0 1

1 1 1

Complementing bits Setting means changing the bits as follow:

0 to 1

1 to 0

Therefore,

Masks for

Changed – 1

Unchanged - 0

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Operands Logic Operations

Original Bit Mask XOR

0 0 0

0 1 1

1 0 1

1 1 0

Use Logic Instructions as Mask

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Examples

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Examples

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Examples

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Other applications of Logic Instructions (1)

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Other applications of Logic Instructions (2)

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NOT Instruction

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TEST Instruction

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Example of Test Instruction

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Exercise (Self-Study)

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Exercise (Self-Study) Contd.

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Thank you.

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