HomeDesign GuideDesign Guide Details
Design Guide Details
Date: 03-01-17

Logic circuits

Few examples of logic devices

Here we list functional diagrams of few logical ICs with the brief description of what they do and also little note on technology advancements

Buffer (non-inverting):

What is buffer?

These devices boost/amplify signal power capabilities by raising the current capacity (both source and drain) but keeping the logic voltage levels same as inputs.

Where used (application): Buffers are used when there requirement to drive multiple devices or higher load device from a single logical output (microcontroller output or any other such logical signal generator). Good example can be you can't connect an LED directly to the output of microcontroller port, buffer can be put in between LED and microcontroller's port.

There are many types of buffers available in the market here below is the connection diagram of 74LCX244.



Connection Diagram


3 to 8 decoder:

What is 3 to 8 decoder?

Decoders have 3 inputs and 8 outputs. The binary input fed at input will be decoded to provide either logical high or low on one of the 8 outputs, which is termed as octal equivalent for that binary input. For a binary input 100, which is 4 in octal number system, the output pin called O4 will go either high or low.

Where used (application): Is used in memory address decoder or any such decoders. Good example is, if a microcontroller has only 8 outputs but you may have to control 32 devices, you can go for this device for such application.

Below is functional diagram and truthtable of one popular decoder 74VHC138 from Fairchild



Based on the required logic functions, building circuits is very easy, you just need to know pin diagram from the datasheet. you hardlly need any other discrete components. So that's the reason only function diagram is given instead of circuit diagrams in this page.

To know other types of logic families please visit the following urls:


Default user
Related Design Guide Articles