Texas Instruments TI-81

Date of introduction:  1990 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:  
Batteries:  4*AAA Date of manufacture:  mth 04 year 1990
AC-Adapter:   Origin of manufacture:  Taiwan
Precision:  13 Integrated circuits:  CPU: Toshiba T6A49
 ROM: ©1990
 RAM: TC5565A
 Display: 2*Toshiba T7778A, T7900
Memories:  0-27    
Program steps:  2400 Bytes Courtesy of:  Joerg Woerner

Some weeks ago, mid of December 2008, Marc Ferrer, a fellow calculator collector living in France, reported an amazing find: A very early TI-81 - manufactured in November 1990 - lacking the backup battery. 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. The TI-Nspire, introduced July 2007, was Texas Instruments' first graphing calculator using non-volatile Flash memory to maintain the information stored in the calculator even with low or empty main batteries.

TI-81_ES_Back.jpg (229864 Byte)We started immediately a research and contacted dozens of TI-81 sellers and buyers on eBay with three questions about the backup battery, serial number and manufacturing code. Within three weeks a seller from Upstate New York reported a TI-81 manufactured in September 1990 lacking the space for the battery with the serial number 093521. Another week later an email from Oregon: Sorry, no serial number, no maunfacturing code and no space for a coin-shaped battery. Bingo!

TI-81_ES_PCB.jpg (426737 Byte)Dismantling the calculator reveals some surprises: 

The main electronics is centered around a Toshiba T6A49 Application
Specific CPU instead the T6A43 found in the final TI-81 calculators.
The display drivers are Toshiba T7778A resp. T7900 chips instead the
later T6A39 resp. T6A40 chips.
We miss indeed the backup battery but the mounting space is obviously
All Intgrated Circuits are manufactured on or before May 1990, long
before the official introduction of the TI-81.

We assume that the featured TI-81 is a rare Engineering Sample that leaked to the market or was used for first acceptance tests at different schools.

TI-81_ES_PCBM.jpg (376248 Byte)Most astonishing to us is the find of the Toshiba T6A49 Application Specific CPU in this early TI-81, the "final" version w/o backup battery manufactured in September 1990 uses a revised T6A49A chip while the common version with backup battery uses a T6A43 chip. We assume that the T6A49(A) had a serious bug and was replaced with the proofen T6A43 from the PS-6600 Organizer. (Comment: The PS-6600 was introduced in 1992, two years after the TI-81.)

TI-81_ES_PCBD.jpg (753642 Byte)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. 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.


TI-81_ES_OS.jpg (58728 Byte)1.0

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, January 27, 2009. No reprints without written permission.