TI99 Environment

CALL_KEY

Syntax

integer-variable=CALL_KEY(keyunit,key,status)

Description

This function scans for a key press on the keyboard. It is TI-99/4A's version of BASIC's INKEY$.
Parameters "key" and "status" are unused, they are mandatory to maintain compatibility with TI programs copied directly from other sources. You can place two unused/dummy variables here.
A keyunit value of 0 scans the entire keyboard. A keyunit value of 1 scans the left side of keyboard and the gamepad controller's fire button (A button). A keyunit value of 2 scans the right side of keyboard and also the gamepad's fire button (A button).

integer-variable and the global variable TIAsc hold the key's ASCII Code (for keyunit 0) or scan code (for key units 1 or 2) of the key pressed. integer-variable can also hold the A-button status of the gamepad controller (key units 1 or 2). If the fire button is pressed on the gamepad, integer-variable and the TIAsc global variable return the value of 18.

on-off conditions

TIKeyStatus global variable holds the actual key press status of Call_Key (possible return values are -1,0,1). If no key has been pressed TIKeyStatus = 0. If a new key is pressed, TIKeyStatus = 1. If the same key was pressed from a previous call, TIKeyStatus = -1. The same values apply to the gamepad controller's fire button status.

Up Arrow key is the equivalent of TI-99's uppercase E = 69
Down Arrow key is the equivalent of TI-99's uppercase X = 88
Left Arrow key is the equivalent of TI-99's uppercase S = 83
Right Arrow key is the equivalent of TI-99's uppercase D = 68

Example Code

` Test of call_key - program to move block character left and right using arrow keys
CALL_CHAR(42,"FFFFFFFFFFFFFFFF")
ROW = 24 : COL = 12 : speed = 50
CALL_HCHAR(ROW,COL,42,1) : TI_SYNC()
mtimer = timer()
do
    _KEYSCAN:
  k = CALL_KEY(0,K,S)
    If TIKeyStatus = 0 OR ( k <> 68) and ( k <> 83)     
        goto _KEYSCAN
    ENDIF
    if timer() > mtimer + speed
        CALL_HCHAR(ROW,COL,32,1)
        if k = 83   ` left
            dec col,1
            if col < 1 then col = maxcols
        else
            if k = 68   ` right
                inc col,1
                if col > maxcols then col = 1
            endif
        ENDIF
        CALL_HCHAR(ROW,COL,42,1)
        mtimer = timer()        
        TI_SYNC()
    endif
LOOP

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