86:Ports:01
From WikiTI
Synopsis
Port Number: 01h
Function: Keyboard Port
This port reads key presses from the keypad. The keypad is divided into a series of groups.
See also TI-83 Plus Port 01, which is identical apart from the key labels & the lack of battery level detection.
Read Values
- Bits are set according whether corresponding keys from selected groups are pressed. Groups are selected through writing to the port. A pressed key reads a 0 bit. An unpressed key reads a 1 bit.
- Bit 0 will also read as 0 if groups 0-2 are all selected & the battery level is low.
Write Values
- FFh : Reset the keypad. This unselects all groups and resets the keypad state.
- F8h : Check battery level. This also selects keypad groups 0-2 for monitoring.
- Anything else : Any 0 bit adds the corresponding group to the list of monitored groups. When a key in a monitored group is pressed, the corresponding key bit reads 0, otherwise it reads 1 (active-low).
Key Map
The key map is laid out as follows:
| Group Bit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ||
|---|---|---|---|---|---|---|---|---|---|---|
| Group Mask | FE | FD | FB | F7 | EF | DF | BF | 7F | ||
| Key Bit | (Mask) | |||||||||
| 0 | (FE) | DOWN | ENTER | (-) | . | 0 | F5 | |||
| 1 | (FD) | LEFT | + | 3 | 2 | 1 | STO | F4 | ||
| 2 | (FB) | RIGHT | - | 6 | 5 | 4 | , | F3 | ||
| 3 | (F7) | UP | * | 9 | 8 | 7 | x2 | F2 | ||
| 4 | (EF) | / | ) | ( | EE | LN | F1 | |||
| 5 | (DF) | ^ | TAN | COS | SIN | LOG | 2nd | |||
| 6 | (BF) | CLEAR | CUSTOM | PRGM | TABLE | GRAPH | EXIT | |||
| 7 | (7F) | DEL | x-VAR | ALPHA | MORE |
- Note: Group FB Key FE is NEGATE, not to be confused with SUBTRACT.
- Note: Group DF Key FE would be ON, but the ON key is tested through Port 03, bit 3.
Comments
- The OS delays about 1400 cycles (100 iterations of a tight DJNZ loop) when checking the battery level at startup, which is much longer than used to test if keys are pressed.
- Bit 0 will be 0 when testing the battery level if the warning message would appear. However, because it is still also wired to the keypad, holding any of DOWN, ENTER, or (-) when turning the calculator on will also cause the warning message to appear.
