The TI89 was the best calculator available when I was in high school, so naturally Bill Orr and I spent a lot of time working with it.
The TI89 is a powerful calculator. It also has an exceptionally cool operating system. This project is a TSR program that reads keypresses from a PS/2 keyboard connected to the link port and sends them to the operating system so that the calculator can be used for new applications that require the use of a keyboard. The difficult task of making the PS2 driver was already done for us by Stephan Effelsberg in his PS2 mouse interface.
TI89 TSR Subcalculator
Sometimes when using a TI89 you may find yourself busy doing an intense computation that takes a long time, but you just need to do a quick calculation right away. If you have the TSRcalc installed then you won't have to abort the process because you can hold down diamond and press ON and a small window will appear where you can do 4-function calculator computations. During this time, the calculator is suspended so that when you press the ESC key, any process will resume exactly where it left off. This TSR is extremely efficient because it is hooked to the ON key interrupt so it uses no CPU time during normal calculator usage.
This is a swivel holster for the TI89 with a translucent gray case. The battery cover is transparent like the silver edition TI83. The swivel mount came from a $1 cell phone holder from Walmart and was attached to the case with epoxy.