computer science

Modified Modular Jack

Modified Modular Jack is a computer 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 Modified Modular Jack rather than just read about it. In short: The Modified Modular Jack (MMJ) is a small form-factor serial port connector developed by Digital Equipment Corporation (DEC). It uses a modified version of the 6P6C modular connector with the latch displaced off-center so that standard modular connectors for telephone jacks cannot accidentally be plugged in.

Key takeaways

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

Reference excerpt

The Modified Modular Jack (MMJ) is a small form-factor serial port connector developed by Digital Equipment Corporation (DEC). It uses a modified version of the 6P6C modular connector with the latch displaced off-center so that standard modular connectors for telephone jacks cannot accidentally be plugged in. MMJ connections are used on Digital minicomputers, such as the PDP-11, VAX and Alpha systems, and to connect terminals, printers, and serial console servers. The MMJ connector has six conductors. As defined by DEC, the six pins are Tx and Rx for the data transmission, their return paths, and DSR and DTR for handshaking. The transmit and receive signals are differential: each signal is the voltage difference between the line and its associated ground, as opposed to a voltage on a single connector relative to a common reference. The electrical signaling is defined by the EIA RS-422 standard. The system can interoperate with RS-232 signaling by shorting the lower voltage sides of each signal to the RS-232 signal ground line. In this case, RS-232 limits apply to data rate and cable length. When connecting two DTE devices such as a computer and a printer, the Digital BC16E crossover cable is used. The DEC VT320 and TI/HP-928 were terminals offering an MMJ option. Using RS-422 signaling over 6-conductor RJ12, cables could be up to 1000 meters. Thrustmaster is using the MMJ connector for connecting its line of rudder pedals and racing pedals to either USB via a proprietary Thrustmaster Adapter, or directly to a joystick or racing wheel. The Lego Mindstorms NXT and EV3 set used connectors similar to MMJ for motors and sensors. This was to prevent the connection of standard telephone cords. The MMJ connector used by LEGO is also taller than those used with data terminals. CEA-909 uses the MMJ connector for control signals to a smart antenna, which can either physically or electrically rotate for maximum signal strength.

Illustrations

Worked examples

Example 1 — a first encounter with Modified Modular Jack

Start with the simplest possible case. Write down what Modified Modular Jack claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer 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 Modified Modular Jack 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 Modified Modular Jack 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 Modified Modular Jack

In research: Modified Modular Jack appears in computer 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 Modified Modular Jack 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: Modified Modular Jack is common in secondary-school and first-year university syllabi. It links to neighbouring topics Networking hardware, so understanding it makes those chapters shorter.
In everyday life: Look for Modified Modular Jack 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 Modified Modular Jack in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Modified Modular Jack 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 Modified Modular Jack out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Modified Modular Jack in simple terms?

Why does Modified Modular Jack matter?

Because it connects several computer 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 Modified Modular Jack?

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 Modified Modular Jack.