logic circuit

Multiplexers

• Multiplexers (MUX) are devices that take data from multiple sources and transmit it over a single line to a single destination.
• They consist of several data inputs (channels), a number of select lines to choose which input to transmit, and a single output channel.
• Input channels can have a single bit or multiple bits, determining the channel width.
• Different multiplexers have different numbers of input channels, which is often denoted as (n-channel x m-bit multiplexer).
• Boolean expressions can be used to describe the output based on the input and selection lines.
• Multiplexers have applications in displaying data, generating logic functions, and parallel-to-serial conversion.
• Some multiplexers feature active low or high outputs, and an enable input for controlling the device.

Problems and Solutions

• Analyze the provided diagrams and figures of multiplexers to understand their channel input/output configurations.
• Evaluate and name multiplexers in diagrams or illustrations to determine their channel/bit characteristics (e.g., "4 Channel x 1-Bit Multiplexer").
• Identify Boolean expressions of multiplexers given the inputs, select lines, and output to solve for logic equations.
• Identify output functions for provided mux diagrams and use this in conjunction with input data to define logic expressions.

Active Low or Active High Outputs

• Some commercial multiplexers have active-low or active-high outputs controlling the device.
• Some devices feature both output types.

Enable Input

• Some multiplexers include enable inputs that regulate overall device activity.
• An active high enable typically means the device only operates when the enable input is high.

Applications

• Multiplexing of Displays (Using a single seven-segment decoder driver to serve several displays)
• Logic Function Generation (Implementing logic operations using multiplexer)
• Parallel to Serial Conversion

The Light Emitting Diode (LED)

• The LED has an anode and a cathode.
• Current flow is from anode to cathode.
• Different LED colors have different typical forward voltages.

Common Anode 7-Segment LED Display

• The common anode configuration has anodes connected together.
• Common cathode configurations have cathodes connected together.

Logic Function Generation

• Multiplexers can implement logic functions with boolean expressions and input/select line combinations.

Implementation

• Provide a Boolean function using an '8-channel x 1-bit multiplexer', and identify the rows in the truth table where the function Z is true.
• Utilize input/select line and output combinations for different functions by an 8-channel x 1-bit multiplexer to build and analyze logic expressions.

Multiplexer Circuitry

• Detailed circuit diagrams of multiplexers often display input channels with different characteristics, showing how logic gates connect and are sequenced for specific outputs.
• Diagrams of various multiplexers showing input/output signals and corresponding truth table configurations illustrate the operational processes of different muxes with their configurations.

Commercial Multiplexers

• Commercial multiplexers (e.g., 54150/DM54150/DM74150, 54151A/DM54151A/DM74151A) are data selectors or multiplexers that perform specific tasks like parallel-to-serial conversion, multiplexing and generating boolean equations.
• Features like data line selections, propagation delays, and power dissipation are important specifications of commercial multiplexers.
• Logic diagrams demonstrate functionality, including data inputs, strobe inputs ("enable"), output sections, and select input connections.

Decoders

• Decoders are logic circuits that activate only one output corresponding to a specific input binary code while the others remain inactive.
• A decoder takes n inputs and produces 2ⁿ outputs with only one output high for a valid input.
• Decoders may be active-high or active-low, denoting when a specific output is activated (high or low, respectively).
• Decoders have applications in logic functions, timing and sequencing, and device control in various systems

Encoders

• Encoders convert a number of inputs to a coded output.
• They perform a "reverse" of decoding tasks.
• Encoders are utilized in many applications such as translating user inputs into coded instructions, and more.
• Priority encoders select the highest-priority input when multiple inputs are active simultaneously.

BCD-to-Decimal Decoders

• These decoders convert BCD code(binary coded decimal) to decimal values.
• These decoders employ NAND gates to ensure low active output.
• Implementation procedures for BCD to decimal decoders frequently use NAND based configurations and provide active low outputs for specific digits.

7-Segment Decoders/Drivers

• These decoders manage LED displays by activating specific segments based on BCD inputs.
• Functionality is more complicated, as multiple input combinations potentially activate the same segment(s).
• The logic complexity and specifications associated with segment decoders frequently rely on active high or active low logic.
• The figures (diagrams) show how different digit displays are generated with 7-segments LED's (Light Emitting Diodes).

HDL

• HDL is a Hardware Description Language used to design and implement digital systems.
• VHDL is one popular form of HDL to specify circuits.
• VHDL contains rules for designing with modules, using variables and constants, operations, and data types.
• HDL offers a procedural language which is used to describe the components in sequential and behavioral manners.
• HDL's allow design entities to be independently checked and tested using simulations which will display the data flow to show behaviour.