engineering

MAX232

MAX232 is a engineering 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 MAX232 rather than just read about it. In short: The MAX232 is an integrated circuit by Maxim Integrated Products, now a subsidiary of Analog Devices, that converts signals from a TIA-232 (RS-232) serial port to signals suitable for use in TTL-compatible digital logic circuits. The MAX232 is a dual transmitter / dual receiver that typically is used to convert the RX, TX, CTS, RTS signals.

Key takeaways

MAX232 belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MAX232 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MAX232 from memory before moving on to harder problems.

Reference excerpt

The MAX232 is an integrated circuit by Maxim Integrated Products, now a subsidiary of Analog Devices, that converts signals from a TIA-232 (RS-232) serial port to signals suitable for use in TTL-compatible digital logic circuits. The MAX232 is a dual transmitter / dual receiver that typically is used to convert the RX, TX, CTS, RTS signals. The drivers provide TIA-232 voltage level outputs (about ±7.5 volts) from a single 5-volt supply by on-chip charge pumps and external capacitors. This makes it useful for implementing TIA-232 in devices that otherwise do not need any other voltages. The receivers translate the TIA-232 input voltages (up to ±25 volts, though MAX232 supports up to ±30 volts) down to standard 5 volt TTL levels. These receivers have a typical threshold of 1.3 volts and a typical hysteresis of 0.5 volts. The MAX232 replaced an older pair of chips MC1488 and MC1489 that performed similar RS-232 translation. The MC1488 quad transmitter chip required 12 volt and −12 volt power, and MC1489 quad receiver chip required 5 volt power. The main disadvantages of this older solution was the ±12 volt power requirement, only supported 5 volt digital logic, and two chips instead of one.

History The MAX232 was proposed by Charlie Allen and designed by Dave Bingham. Maxim Integrated Products announced the MAX232 no later than 1986.

Versions The later MAX232A is backward compatible with the original MAX232 but may operate at higher baud rates and can use smaller external capacitors – 0.1 μF in place of the 1.0 μF capacitors used with the original device. The newer MAX3232 and MAX3232E are also backwards compatible, but operates at a broader voltage range, from 3 to 5.5 V. Pin-to-pin compatible versions from other manufacturers are ICL232, SP232, ST232, ADM232 and HIN232. Texas Instruments makes compatible chips, using MAX232 as the part number.

Voltage levels

The MAX232 translates a TTL logic 0 input to between +3 and +15 V, and changes TTL logic 1 input to between −3 and −15 V, and vice versa for converting from TIA-232 to TTL. (The TIA-232 uses opposite voltages for data and control lines, see RS-232 voltage levels.)

Applications

The MAX232(A) has two receivers that convert from RS-232 to TTL voltage levels, and two drivers that convert from TTL logic to RS-232 voltage levels. As a result, only two out of all RS-232 signals can be converted in each direction. Typically, the first driver/receiver pair of the MAX232 is used for TX and RX signals, and the second one for CTS and RTS signals. There are not enough drivers/receivers in the MAX232 to also connect the DTR, DSR, and DCD signals. Usually, these signals can be omitted when, for example, communicating with a PC's serial interface, or when special cables render them unnecessary. If the DTE requires these signals, a second MAX232 or some other IC from the MAX232 family can be used.

Derivatives The MAX232 family was subsequently extended by Maxim to versions with four transmitters (the MAX234) and a version with four receivers and four transmitters (the MAX248), as well as several other combinations of receivers and transmitters. A notable addition is the MAX316x which is able to be electrically reconfigured between differential 5 V (RS-422 and RS-485) and single-ended RS-232 albeit at reduced voltage.

References

Illustrations

Worked examples

Example 1 — a first encounter with MAX232

Start with the simplest possible case. Write down what MAX232 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, 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 MAX232 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 MAX232 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 MAX232

In research: MAX232 appears in engineering 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 MAX232 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: MAX232 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Integrated circuits, so understanding it makes those chapters shorter.
In everyday life: Look for MAX232 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 MAX232 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MAX232 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 MAX232 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MAX232 in simple terms?

Why does MAX232 matter?

Because it connects several engineering 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 MAX232?

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 MAX232.