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Digital Logic & Design

Dr. Sajjad Ahmed Nadeem

Department of Computer Science & IT University of Azad Jammu & Kashmir

Muzaffarabad

Module-04 � Registers. � Register Transfer. � Binary Logic. � Gates.

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Registers

Functions of Commonly used Registers

(IR)

(AC)

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Register Transfer � The CU uses Registers to keep track of

various computer sequences. � Every input or output device must have at

least one register to store the information transferred to or from the device. � An inter-register transfer operation, a

basic operation in digital system, consists of a transfer of the information stored in one register to another.

Register Transfer

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Register Transfer � The input unit is assumed to have a

keyboard, a control unit, and an input register. � Each time a key is struck, the control

enters into the input register an equivalent 8 bit alphanumeric character code (assume code is ASCII). � The information from the input register is

transferred into the eight least significant cells of a processor register.

Register Transfer � After every transfer, the input register is cleared

to enable the control to insert a new 8 bit code when the keyboard is struck again. � Each 8 bit character transferred to the

processor register is preceded by a shift of the previous character to the next 8 cells on its left. � When the transfer of characters is completed,

the processor register is full, and its contents are transferred into a memory register.

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Register Transfer � To process discrete quantities of information in

binary form, a computer must be provided with, i. Devices that hold the data to be processed. ii. Circuit elements that manipulate individual bits of information. � The device most commonly used for holding

data is register. � Manipulation of binary variables is done by

means of digital logic circuits.

Register Transfer

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Register Transfer � Process of adding two 10 bit binary numbers. � Memory unit, which normally consists of

thousands of registers, is shown with only 3 of its registers. � Processor is shown with 3 registers, R1,R2,R3,

together with Digital Logic Circuit that manipulate the bits of R1 and R2 and transfer into R3, their sum.

Register Transfer � Information stored in memory can be

transferred to processor registers, and Results obtained in processor registers can be transferred back into a memory register for storage. � The registers of a system are the basic elements

for storing and holding the binary information. � The Digital Logic Circuits process the

information.

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Binary Logic

� Binary Logic deals with variable that take on two discrete values and with operations that assume logical meaning. � Binary logic is used to describe in a

mathematical way, the manipulation and processing of binary information. � It is particularly suited for the analysis and

design of digital systems. � It is also termed as Boolean Algebra.

Boolean Algebra

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Operator Precedence

Binary logic � Binary logic deals with variables that take on two

discrete values and operations that assume logical meaning.

� Logic gates: electronic circuits that operate on one or more input signals to produce an output signal.

� Example x y x AND y 0 0 0 0 1 0 1 0 0 1 1 1

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Electrical signals

Two values: 0 or 1

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Symbols for digital logic circuits

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Input-Output signals for gates

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Gates with multiple inputs