Chapter 4 Combinational Logic Circuits

Digital Electronic Technology Chapter 4 Combinational logic circuit mind map, including analysis methods of combinational logic circuits, commonly used combinational logic circuits, design methods of combinational logic circuits, and competition-adventure phenomena in combinational logic circuits.

Edited at 2022-04-10 18:04:17

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Chapter 4 Combinational Logic Circuits

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Outline

Chapter 4 Combinational Logic Circuit\

4.1 Analysis methods of combinational logic circuits

①Write logical expressions ②Simplify ③Real value table ④Analyze

Example:

half adder

full adder

4.2 Commonly used combinational logic circuits

decoder

Decoding: "Translate" the input code into another code output. and the reverse process of the encoder.

2-wire to 4-wire decoder (74HC139)

3-wire to 8-wire decoder (74HC138)

Two 2-wire-4-wire decoders connected to form a 3-wire-8-wire decoder

P.111 on

4-line to 16-line decoder (74HC154)

Use two 3-line to 8-line decoders 74HC138 to form a 4-line to 16-line decoder

Seven-segment display decoder

Encoder

Encoding: Compile each signal of a set of encoding inputs into a corresponding output code.

Ordinary encoder: Only one encoding signal is allowed to be input during normal operation, and more than two encoding input signals are not allowed to be input at the same time, otherwise the output will be in an error state.

Priority encoder: When there are more than two encoding input signals at the same time, only the one with the highest priority is encoded.

8-wire-3-wire priority encoder

data selector

Select one from a set of input data and send it to the output

Dual four-to-one data selector (74HC153)

Eight-select one data selector connected by two four-select one data selectors

Eight-to-one data selector (74HC151)

Adder

half adder

full adder

Numeric comparator

One bit numerical comparator

Multi-bit numerical comparator

Principle: Compare from the high digit, and only compare the next digit if the high digit is equal.

4.3 Design methods of combinational logic circuits

1. Logical abstraction Analyze causal relationships, determine input/output variables, cause-input, result-output Define the meaning of logical state (assignment), the specific meaning of 1 and 0 List truth table 2. Write the logical function expression from the truth table 3. Select the type of device 4. Simplify or transform logical expressions 5. Draw logic diagrams from logical expressions

Select commonly used combinational logic circuits for medium-scale integration

①Select data selector

②Choose a decoder

4.4 Competition-hazard phenomenon in combinational logic circuits

Competition does not necessarily involve risk, but risk must involve competition

Tangent Carnot circles create adventure. Elimination method: Add tangent Carnot cycles