| S1 | S2 | S3 | Mode | Description |
| Off | Off | Off | 0 | Normal (four-function calculator) |
| Off | Off | On | 1 | Demo (time/date/temperature display) |
| Off | On | Off | 2 | RPN Coprocessor |
| Off | On | On | 3 | Serial LED display |
| On | Off | Off | 4 | Serial LCD |
| On | Off | On | 5 | AOS Calculator |
| On | On | Off | 6 | RPN Calculator |
| On | On | On | 7 | Forth |
Table 2—Modes 1, 2, 5, and 7 have not been implemented. Activate the remaining modes using C compiler flags and the selected application files (calc1.c, hp45.c, or mathtst.c). The mode switch selection is not available.