Texas Instruments TI-85

Date of introduction:  March 1992 Display technology:  LCD dot matrix
New price:  $130 Display size:  8 * 21 characters
Size:  6.8" x 3.1" x 0.85"
 172 x 80 x 21 mm3
Weight:  5.8 ounces, 172 grams Serial No:  1022092
Batteries:  4*AAA + CR1620 Date of manufacture:  mth 10 year 1992
AC-Adapter:   Origin of manufacture:  Taiwan (I)
Precision:  14 Integrated circuits:  CPU: Toshiba T6A43
 ROM: TC541001AF
 RAM: SRM20256
 Display: 2*T6A39,
Program steps:  28k Bytes Courtesy of:  Joerg Woerner

TI-85_I1092_Back.jpg (264353 Byte)The TI-85 followed the famous TI-81 and sports a larger user memory. The size of the display was increased to 64 * 128 pixel.

The main features of the TI-85 in a short summary:

Graphing of up to 99 functions at one time.
Parametric graphing to analyze up to three parametric equations.
Manipulation of three matrices with dimensions of 30*30.
One- and two-variable statistical analyses with up to 2,800 data points.
Up to 37 programs with a total of 28,000 Bytes.

TI-85_I1092_PCB.jpg (438960 Byte)Dismantling the TI-85 reveals no big surprises: The main electronics is centered around the well-known Toshiba T6A43 Application Specific CPU, the 8k Bytes Static RAM (SRAM) chip used in the TI-81 was replaced with a larger 32k Bytes chip and the capacity of the ROM (Read-Only Memory) was doubled from 64k Bytes to 128k Bytes.

It makes use of just six main components on the printed circuit boards (PCBs):

CPU (Central processing Unit): The Toshiba T6A43 is a so-called Application Specific CPU and combines a Z80 core with an ASIC (Application Specific Integrated Circuit). You’ll find different approaches within the graphing calculator line of Texas Instruments, sometimes the use of an individual CPU (e.g. Z80 and M68000) with a supporting ASIC or – like with this TI-85 - the integration of the CPU into the ASIC. Learn more about the Hardware Architecture of TI’s Graphing Calculators.

TI-85_I1092_PCBM.jpg (284831 Byte)ROM (Read Only Memory): The ROM contains the operating system of the calculator. The first products on the market used mask-programmable ROMs, the program was stored already during the production of the Integrated Circuit. Later calculators changed to Flash ROMs, a technology allowing the programming of the software during the final production stage of the calculator. With the TI-83 Plus and all later graphing calculators from Texas Instruments even the user was able to reprogram the operating system.

This TI-85 manufactured already in October 1992 makes use of an OTP-ROM (One-time Programmable Read-Only Memory) Toshiba TC541001AF. Later TI-85 calculators host a Mask ROM LH531 manufactured by Sharp, Japan. It is common practice in software engineering to avoid the high one-time costs and long lead time of a Mask-ROM during the ramp up of a new product. One-time programmable ROM like the TC541001 are on the other hand more expensive.

TI-85_I0892_PCBM.jpg (220404 Byte)In the meantime we discovered a TI-85 manufactured in August 1992, sporting a LH531 Mask ROM, too. Unfortunately doesn't the calculator turn on, we don't know the ROM-Version of this particular calculator.

RAM (Random Access Memory): The RAM is used as data memory and is used to store both variables, user programs and intermediate results. This TI-85 makes use of SRM20256 manufactured by Suwa Seikosha, Japan. The capacity of the memory is 32k Bytes.

TI-85_I1092_PCBD.jpg (879638 Byte)DISPLAY: The two Toshiba T6A39 are column drivers for small-to-medium-sized dot matrix graphic LCD’s, while the T6A40 is a row driver. They are compatible with Z80 based CPU’s and drives displays with up to 80 columns, resp. 68 rows. The display size of the TI-85 is 128 * 64 pixel, therefore a total of three drivers are necessary.


A special "teacher version" called TI-85 VSC combines the standard TI-81 features with a fixed connection to a ViewScreen panel via a flat-ribbon cable. Placing the panel on the overhead projector enlarges the image of the handheld screen so that each student can follow along.

In 1995 the appearance of the TI-85 was slightly changed, search the position of the TI-logo here. Don't miss the restyled TI-81 and TI-82.

A serial port of the calculators allows the connection to the Calculator-Based Laboratory system CBL, its successor CBL 2, the Calculator-Based Ranger CBR and its successor CBR 2.

About one year later with the TI-86 a even more powerful successor was introduced.


TI-85_I1092_OS.jpg (39764 Byte)1.0

You can check the ROM version of your TI-85 using the following key sequence and reading the number on your screen:

[2nd] [MODE] [ALPHA] [S]

Information provided by and Xavier Andréani.

Exam acceptance:

The TI-85 is permitted (as of September 27, 2007) for use on SAT, ACT, PSAT and AP exams.

The TI-85 is featured in the Texas Instruments Incorporated sales catalog CL-1233 dated 1994.


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© Joerg Woerner, May 3, 2003. No reprints without written permission.