science

Wired logic connection

Wired logic connection is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Wired logic connection rather than just read about it. In short: A wired logic connection is a logic gate that implements boolean algebra (logic) using only passive components such as diodes and resistors. A wired logic connection can create an AND or an OR gate.

Key takeaways

Wired logic connection belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Wired logic connection to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Wired logic connection from memory before moving on to harder problems.

Reference excerpt

A wired logic connection is a logic gate that implements boolean algebra (logic) using only passive components such as diodes and resistors. A wired logic connection can create an AND or an OR gate. Limitations include the inability to create a NOT gate, the lack of amplification to provide level restoration, and its constant ohmic heating for most logic (particularly more than CMOS) which indirectly limits density of components and speed. Wired logic works by exploiting the high impedance of open collector outputs (and its variants: open emitter, open drain, or open source) by just adding a pull-up or pull-down resistor to a voltage source, or can be applied to push–pull outputs by using diode logic (with the disadvantage of incurring a diode drop voltage loss).

Active-high wired AND connection

The wired AND connection is a form of AND gate. When using open collector or similar outputs (which can be identified by the ⎐ symbol in schematics), wired AND only requires a pull up resistor on the shared output wire. In this example, 5V is considered HIGH (true), and 0V is LOW (false). This gate can be easily extended with more inputs. When all inputs are HIGH, they all present high impedance, and the pull-up resistor pulls output voltage HIGH, but if any input is LOW, they pull the output LOW:

When driving a load, the HIGH output is reduced by the pull-up's voltage drop, though the LOW output is almost 0V. But if diode logic is used, each input requires a diode, and the LOW output voltage will additionally be raised by the diode's forward voltage. Care should be taken to ensure the output still lies within valid voltage levels.

Active-high wired OR connection

The wired OR connection electrically performs the Boolean logic operation of an OR gate using open emitter or similar inputs (which can be identified by the ⎏ symbol in schematics) connected to a shared output with a pull-down resistor. This gate can also be easily extended with more inputs. When all inputs are LOW, they all present high impedance, and the pull-down resistor pulls the output voltage LOW, but if any input is HIGH, they pull the output HIGH:

When driving a load, the LOW output is raised by the pull-down's voltage drop, though the HIGH output is almost the supply voltage (5V). But if diode logic is used, each input requires a diode, and the HIGH output voltage will additionally be lowered by the diode's forward voltage.

Reversing active level An active-high wired AND can be treated as active-low wired OR (and an active-high wired OR can be treated as active-low wired AND), by using active-low logic (or negative logic) and applying De Morgan's laws.

Compatibility of wired AND OR using diodes

Diode logic uses a diode for each input in addition to a shared pull-up resistor (for wired AND) or a pull-down resistor (for wired OR). However, each stage of diode logic reduces output voltage levels. So without amplification, the output voltage may not be compatible with the primary logic family.

References

Digital Techniques, Heathkit Educational Systems,1990 Fundamental Physics, K.L Gomber and K.L Gogia, Pradeep Publications, 2005

External links Configuring NI 6xxx Devices for Wired-OR (Open Collector) Output Mode In LabVIEW – An Introduction to Wired-OR Outputs and Open-Collector Circuits

Illustrations

Worked examples

Example 1 — a first encounter with Wired logic connection

Start with the simplest possible case. Write down what Wired logic connection claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Wired logic connection before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Wired logic connection ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Wired logic connection

In research: Wired logic connection appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Wired logic connection in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Wired logic connection is common in secondary-school and first-year university syllabi. It links to neighbouring topics Logic gates, so understanding it makes those chapters shorter.
In everyday life: Look for Wired logic connection outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Wired logic connection in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Wired logic connection means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Wired logic connection out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Wired logic connection in simple terms?

A wired logic connection is a logic gate that implements boolean algebra (logic) using only passive components such as diodes and resistors. A wired logic connection can create an AND or an OR gate.

Why does Wired logic connection matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Wired logic connection?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Wired logic connection.