Logic ICs take two or more digital input signals and combine these input signals in a logical manner, producing a new digital output signal.
Logic ICs can perform fundamental low-level logic operations such as AND, OR, XOR, NOT, may process sequence of signals (as in FlipFlops or Counters), or even apply soophisticated signal processing (as in Encoders).
All of these logic operations can also be performed in software, so in microcontroller-based projects, logic level ICs are much less often used. However, even with microcontrollers, logic level ICs may be used for two primary reasons:
- Speed: as hardware devices, signal processing is much faster compared to software solutions
- Simplicity: can shift complexity away from firmware: it may just be simpler to add a hardware logic IC in your circuitry to solve a challenge rather than having to deal with signal processing in firmware.
Groups Of Logic ICs
Here are a few of the more popular logic ICs:
- Logic Gates: perform fundamental logic operations (see next section for details)
- Buffers: strengthen or isolate signals to prevent signal degradation and ensure proper transmission across circuits. They are used to interface between different parts of a circuit, protecting against signal loss or interference.
- FlipFlop: bistable devices that store a single bit of data, with two stable states (0 and 1). They are used for creating memory elements, counters, and registers in digital systems, as they can “flip” between states based on input signals.
- Counters: sequential logic circuits that count pulses, typically in binary or decimal form. They are widely used in time-keeping, event counting, frequency division, and digital clocks.
- Shift Registers: shift data bits in or out of a register, serially or in parallel. They are essential in data storage, transfer, and conversion between serial and parallel formats, often used in communication systems.
- Adders: arithmetic circuits that perform binary addition, often forming the basis for arithmetic logic units (ALUs) in processors. They add binary numbers and are essential for all computational tasks in digital electronics.
- Timers: generate precise time delays, oscillations, and pulse-width modulated signals. They are used in timing applications, like setting delays, generating clocks, and creating waveform signals in various digital circuits.
- Multiplexers: select one of many input signals and forward it to a single output, while demultiplexers take a single input and route it to one of many outputs.
- Encoders/Decoders: convert multiple input lines into a smaller number of outputs, typically binary code, while decoders perform the reverse, converting binary inputs into a larger number of outputs. They are key in data encoding, communication, and address decoding in memory systems.
Logic Gates
- AND: high when both inputs are high, else low
- NAND: inverted AND. low when both inputs are high, else high
- OR: high when at least one input is high, else low
- NOR: inverted OR. low when at least one input is high, else high
- XOR: high when exactly one input is high, regardless which, else low
- XNOR: inverted XOR. low when exactly one input is high, regardless which, else high
- NOT: reverses logic level, has just one input
AND Gate
| A | B | A AND B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
NAND Gate
| A | B | A NAND B |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
OR Gate
| A | B | A OR B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
NOR Gate
| A | B | A NOR B |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
XOR Gate
| A | B | A XOR B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
XNOR Gate
| A | B | A XNOR B |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
NOT Gate
| A | NOT A |
|---|---|
| 0 | 1 |
| 1 | 0 |
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(content created Aug 28, 2024)