Texas Instruments TI-81

Date of introduction:  1991 Display technology:  LCD dot matrix
New price:  $110 Display size:  8 * 16 characters
Size:  6.8" x 3.1" x 0.85"
 172 x 80 x 21 mm3
Weight:  5.8 ounces, 172 grams Serial No:  0917651
Batteries:  4*AAA Date of manufacture:  mth 09 year 1991
AC-Adapter:   Origin of manufacture:  Taiwan (I)
Precision:  13 Integrated circuits:  CPU: Toshiba T6A43
 ROM: ©1991
 RAM: LH5160
 Display: 2*Toshiba T7778A, T7900
Memories:  0-27    
Program steps:  2400 Bytes Courtesy of:  Joerg Woerner

We recently acquired this unique TI-81 manufactured in September 1991 and discovered some interesting features:

The calculator still lacks a backup battery but sports on the backside of the sales package the "Constant Memory™" feature. Please remember: The TI-81, like all Texas Instruments graphing calculators including even the latest TI-84 Plus Silver Edition, store the user program, user data and even calculator and display settings in a volatile C-MOS memory. To avoid the lost of the memory while replacing the main batteries, the mentioned calculators use an additional, coin-shaped, backup battery. Please read the warning in the 1st edition of the TI-81 Graphics Calculator Guidebook.

Dismantling this TI-81 manufactured in Fall 1991 reveals the next surprise. We expected - based on the experience from an earlier TI-81 manufactured in Fall 1990 and the rare TI-81 Engineering Sample - the Toshiba T6A49A Application Specific CPU. Instead we discovered the proofen T6A43 from the PS-6600 Organizer, used in the more common TI-81 version with backup battery.

Comparing the display boards of different TI-81 models reveals almost identical printed circuit boards (PCBs) populated with either the Toshiba T7778A column drivers and T7900 row drivers or the probably identical T6A39 and T6A40 chips. 

Early in 1992 the internal construction of the TI-81 was revised and missing backup battery was added. Please find a detailed overview of the different hardware architectures of the TI-81 generations between 1990 and 1995 here.

Fellow collectors - if you own a TI-81 w/o backup battery  please report us the serial number and date code from the back of the calculator plus the ROM-Version for our TI-81 1st gen Database.

Don't miss a rare TI-81 Engineering Sample, manufactured probably in April 1990. 



TI-81_I0991_OS.jpg (49767 Byte)1.6K

You can check the ROM version of your TI-81 using the following key sequence and reading the number on your screen:

[2nd] [TEST] [ALPHA] [S]

Information provided by and Xavier Andréani.

Exam acceptance:

The TI-81 is permitted (as of September 27, 2007) for use on SAT, ACT, PSAT and AP exams but is not recommended for the AP exam.  

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If you have additions to the above article please email:

© Joerg Woerner, March 16, 2003. No reprints without written permission.