Texas Instruments TI-85

Date of introduction:  January 1995 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:  27074117
Batteries:  4*AAA + CR1620 Date of manufacture:  mth 03 year 1995 (G)
AC-Adapter:   Origin of manufacture:  Taiwan (I)
Precision:  14 Integrated circuits:  CPU: Toshiba T6A43
 ROM: LH531©1993
 RAM: SRM20256
 Display: 2*T6A39,
Program steps:  28k Bytes Courtesy of:  Joerg Woerner

TI-85_I0395_P1.jpg (342047 Byte)Texas Instruments changed in 1995 the design of the TI-81, TI-82 and TI-85 slightly, please notice the position of the TI-logo and the color of the type designator. The featured calculator was manufactured in March 1995, two years before it was discontinued in 1997.

TI-85_I0395_PCB.jpg (410172 Byte)TI-85_I0395_Back.jpg (296543 Byte)Dismantling the TI-85 reveals only minor changes compared to a very early calculator manufactured already in October 1992: The connector of the serial port was moved slightly and the OTP ROM (One-time Programmable Read-Only Memory) replaced with a Mask ROM.

The calculator electronics makes still use of six main components on the printed circuit boards (PCBs):

TI-85_I0395_ASIC_Z6.jpg (252667 Byte)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 approached 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_I0395_PCBM.jpg (226191 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. 

The Mask ROM LH531GP0©1993 of this TI-85 was manufactured by Sharp, Japan. Please notice the late Copyright of the ROM, the TI-85 was introduced in 1992. We noticed in early TI-85 calculators a one-time programmable ROM TC541001 manufactured by Toshiba.

RAM (Random Access Memory): The Static 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_I0395_PCBD.jpg (578493 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 serial port of the calculators allows the connection to the Calculator-Based Laboratory system CBL and the Calculator-Based Ranger CBR

The TI-85 was within 2 years replaced with the TI-86.


TI-85_I0395_OS.jpg (39336 Byte)7.0

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.


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If you have additions to the above article please email:

© Joerg Woerner, December 5, 2001. No reprints without written permission.