Informasi dari planet: BAB 7. FUNGSI KOMBINASI LOGIKA

Basic Adder

Adder are important in computers and also in other types of digital systems in which numerical date are processed.

Definition : The half-adder accepts two binary digits on its inputs and produces two binary digits on its outputs, a sum bit and a carry bit.

Half-Adder Logic

The Full-Adder

Definition : The Full-Adder accepts two input bits and an input carry and generates a sum output and an output carry The basic different between a full-adder and a half-adder is that the full-adder accepts an input carry.

Full Adder from Two Half-Adder Circuits

Parallel Binary Adder

A single full-adder is capable of adding two 1-bit numbers and an input carry. To add binary numbers with more than one bit, we must use additional full-adders.

Four-Bit Parallel Adders

Truth Table for a 4-Bit Parallel Adder

Adder Expansion

Comparators

The basic function of a comparator is to compare the magnitude of two binary quantities to determine the relationship of those quantities

1-Bit Comparator

The output is 1 when the inputs are equal

2-Bit Comparator

The output is 1 when A0 = B0 AND A1 = B1

4-Bit Comparator

One of three outputs will be HIGH:

- A greater than B (A > B)

-A equal to B (A = B)

-A less than B (A < B)

To determine an inequality of binary numbers A and B,first the highest order bit in each number. The following conditions are possible:

1. If A3 = 1 and B3 = 0, number A is greater than number B

2. If A3 = 0 and B3 = 1, number A is less than number B

3. If A3 = B3 then you must examine the next lower bit position for an inequality

Decoders

Binary decoder

The output is only what we want!

The output is 1 only when:

A0 = 1

A2 = 0

A3 = 0

A4 = 1

The 4-Bit Decoder

In order to decode all possible combinations of 4-bits, sixteen gates are required (2 4 = 16). This type of decoder is commonly called either 4-line-to-16-line decoder or 1-of-16 decoder.

The BCD-to-Decimal Decoder

The BCD-to-decimal converts each BCD code into one of ten possible decimal digit indications. It is frequently referred as 4- line-to-10- line decoder or a 1-of-10 decoder. The method of implementation is the same as for the 1-of-16 decoder.

The BCD-to-7 Segment Decoder

The BCD-to-7-segment decoder accepts the BCD code on its inputs and drive 7-segment display devices to produce a decimal readout.

Encoders

An encoder is a combinational logic circuit that essentially performs a “reverse” decoder function.

The Decimal-to-BCD Encoder

8-Line-to-3-Line Encoder

Multiplexer (Data Selectors)

A multiplexer (MUX) is a device that allows digital information from several sources to be routed onto a single line for transmission over that line to a common destination.
The basic multiplexer has several data-input lines and a single output line.
It also has data-select inputs, which permit digital data on any one of the inputs to be switched to the output line.

1-of-4 data MUX