Texas Instruments TI-85


Brand: Texas Instruments
Model: TI-85
Type: Graphical programmable scientific calculator
Picture: TI-85
Batteries: AAA x 4 + CR 1616 or CR1620 x 1 (memory backup)
Lifetime: Introduced: 1992
Terminated: unknown
Notes: According to this Wikipedia article (link valid 2024-01-13) this is the second Graphical Calculator designed by Texas Instruments, the first one being the T-81. Funny how following this, the TI-83 and especially the TI-84 became a series of calculators in their own league. A variant of the TI-84 was still the standard prescription when my children went to secondary school.

I have never seen the TI-81, but looking at this TI-85, all the basics of the following series are already there. In fact most of what is present on the TI-85, like its menu structure and graphing capabilities are standard issue on modern Graphical Calculators.

TI-85 sine display The calculator has, of course, graphing abilities (even polar) but is also able to do matrix operations and lists, vector operations, BASE conversion, has an equation solver (with up to 10 simultaneous linear equations), named variables (up to eight characters per name), replay, complex numbers, statistics, string operations, a Greek character set, a database of 15 built-in and user defined constants, and of course programmability with all the necessary flow control. Displayed here is a plot of the sine function.

There is also a CATALOG function to list all of the calculator’s commands. Reminds me of the HP 41 series of calculators where this was a Very Cool function to play with.

The "ALPHA"-key takes getting used to, pressing it twice will lock the calculator into "ALPHA" mode. Lock into lower-case alpha by either pressing "ALPHA" followed by "2nd" and "ALPHA", or "2nd" "ALPHA" followed by "2nd" "ALPHA". Press "ALPHA" when locked in "ALPHA" mode to switch between lowercase and uppercase.

While this can not be seen on my scan, the display is slightly tilted for better readability. Its contrast can be changed using "2nd" with the "" and "" arrow keys.

This calculator has an internal accuracy of 14 digits and a 3 digit exponent. It runs on a Zilog Z80 processor and machine language programming was possible by modified backups made using the TI-85 LINK option (see Wikipedia (link valid 2024-01-13)). Its RAM is quite large at 32 kB.

Thank you Thera! Thank you very much, Thera van der Aa, for finding this calculator in a second hand store and donating it to the museum! Thank you as well for the nice illustration at the back of the enveloppe. I couldn’t just throw such an enveloppe away and had to scan and display it! :-)


At the bottom of the calculator there is a little plug socket for The TI-85 LINK. This can be used to communicate between TI-85’s but also for communication with a PC or Apple Macintosh using a serial protocol.