R3 is a 3D graphing application built from the C toolchain for the TI84PCE Calculator. While its feature set is quite limited at the moment, it shows that 3D graphing is indeed possible on the TI84PCE, albeit somewhat slow due to the limited processing power.
Enter your desired equation in reverse-polish notation (postfix notation), and select 'graph'
Use the shunting-yard algorithm to get expressions into postfix notation. For example, x^2 - y^2 becomes x 2 ^ y 2 ^ -.
Since I am working on Cuboid, a 3D graphics library for the CE, this project is currently deprecated, and will eventually be re-worked to utilize Cuboid. However, feel free to browse the code and contribute/improve on this if you like.