83Plus:Ports:01

Synopsis

Port Number: 01h

Function: Keyboard Port

This port controls the on-calc keypad. The keypad is divided into a series of groups.

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. The port reads FF after a reset (write FF).

Write Values

• $FF : Reset the keypad. This unselects all groups and resets the keypad state.
• 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 1.

Comments

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  |     |GRAPH|     |
1 (FD)                    | LEFT|  +  |  3  |  2  |  1  | STO |TRACE|     |
2 (FB)                    |RIGHT|  -  |  6  |  5  |  4  | LN  |ZOOM |     |
3 (F7)                    | UP  |  *  |  9  |  8  |  7  | LOG |WIND |     |
4 (EF)                    |     |  /  |  )  |  (  |  ,  | x^2 | Y=  |     |
5 (DF)                    |     |  ^  | TAN | COS | SIN |x^-1 | 2nd |     |
6 (BF)                    |     |CLEAR|VARS |PRGM |APPS |MATH |MODE |     |
7 (7F)                    |     |     |     |STAT |X,T..|ALPHA| DEL |     |

NOTE: Group FB Key FE is NEGATE, not to be confused with SUBTRACT. NOTE: Group DF Key FE could be ON, but the ON key is tested elsewhere (a "special case" key - after all, it is the ON key).

Example

ld a, 0FFh ;Reset the keypad.
out (1), a
ld a, 0FEh ;Select group 0.
out (1), a
in a, (1) ;Test for keys.
and 0FDh ;Test for Left Arrow key by making A 0 if left was pressed.
call z, LeftArrowPressed ;If 0 then left was pressed.
ld a, 0FFh ;Reset the keypad.
out (1), a