computer science

TI-85

TI-85 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 TI-85 rather than just read about it. In short: The TI-85 is a graphing calculator made by Texas Instruments and is powered by a Zilog Z80 microprocessor, as used in the TI-73 and TI-81 to TI-86. Designed in 1992 as TI's second graphing calculator (the first was the TI-81), it was replaced by the TI-86, which has also been discontinued.

Key takeaways

TI-85 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 TI-85 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TI-85 from memory before moving on to harder problems.

Reference excerpt

The TI-85 is a graphing calculator made by Texas Instruments and is powered by a Zilog Z80 microprocessor, as used in the TI-73 and TI-81 to TI-86. Designed in 1992 as TI's second graphing calculator (the first was the TI-81), it was replaced by the TI-86, which has also been discontinued. The TI-85 was significantly more powerful than the TI-81, as it was designed as a calculator primarily for use in engineering and calculus courses. Texas Instruments had included a version of BASIC on the device to allow programming. Each calculator came with a cable to connect calculators (simply a three-conductor cable with 2.5 mm phone connectors on each end). Another cable known as the TI-Graph Link was also sold, along with appropriate software, to connect the calculator to a personal computer. These cables made it possible to save programs and make backups.

Assembly programs Enthusiasts analyzed memory backups and discovered that entries in the calculator's CUSTOM menu pointed at specific memory locations. With this knowledge, a hack was devised where a special string could be inserted into the backup at the proper location to allow the calculator to execute assembly language programs. These programs could run much faster than their BASIC counterparts and be much more efficient in terms of memory usage. This development made the TI-85 the first TI graphing calculator that could execute assembly programs. Programs written in assembly would be stored as string expressions and accessed through the CUSTOM menu. Games such as Tetris and Boulder Dash are available, as are programs with more practical uses, such as versions of the periodic table. Total memory capacity was about 32 kilobytes, with 28226 bytes available for use. The assembly language shell ZShell is also available for the TI-85. Probably in response to the widespread use of assembly programs, TI officially introduced assembly access in later models, such as the TI-83 and TI-86, along with expanded memory. The TI-86 is very similar to the TI-85, sharing the same display resolution (128×64), processor, and processor speed (6 MHz).

Technical specifications CPU: Zilog Z80 CPU, 6 MHz RAM: 32 KB, (28 KB user-available) ROM: 128 KB non-upgradeable Display Text: 21×8 characters Graphics: 128×64 pixels, monochrome Link capability: 2.5 mm I/O port Power: 4×AAA, 1×CR1616 or CR1620 (for backup power) Programming language(s): TI-BASIC, Z80 Assembly (accessible with a hack)

See also Comparison of Texas Instruments graphing calculators

References

External links ticalc.org – The largest archive of TI programs available. CalcG.org – Very organized and large archive of games and programs. TI-85 Graphical Demo – An interesting graphical demo programmed for a TI-85.

Illustrations

Worked examples

Example 1 — a first encounter with TI-85

Start with the simplest possible case. Write down what TI-85 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 TI-85 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 TI-85 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 TI-85

In research: TI-85 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 TI-85 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: TI-85 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer-related introductions in 1992, Graphing calculators, Texas Instruments programmable calculators, so understanding it makes those chapters shorter.
In everyday life: Look for TI-85 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 TI-85 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TI-85 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 TI-85 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TI-85 in simple terms?

Why does TI-85 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 TI-85?

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 TI-85.