Difference between revisions of "83Plus:Ports:01"

Revision as of 14:50, 27 March 2005

Synopsis

Port Number: 01h

Function: Keyboard Port

This port reads key presses from the 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).
• Note: Group EF Key BF (APPS) is called MATRIX on the TI-83.

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