In 1981, Bill Hogue wrote Robot Attack, a variation on the arcade game Berzerk. Unlike most TRS‑80 games, in Robot Attack you can move and fire in all directions. You fire in a direction by moving the joystick in that direction and pressing the FIRE button. This shows up a problem with the STICK-80 mapping; how can a game determine if the player was moving the joystick up or down and firing if the FIRE button is mapped to a combination of UP plus DOWN?
The solution was to use a discrete bit for the fire button. Big Five Software created the TRISSTICK, their own Atari joystick interface which used bit 4 for the FIRE button. For those who already had the STICK-80, the instructions for Robot Attack contain very detailed instructions about how to modify the joystick’s FIRE button to work with Robot Attack. You don’t normally find instructions for trace cutting and soldering in game documentation!
The TRISSTICK became very popular, and it was a rare TRS‑80 game that was not modified to work with either the STICK-80 or the TRISSTICK. Later on, Big Five also sold a Model 3 version of the TRISSTICK.