This will show you how to use the _getkey ROM call
_Getkey is a ROM call similar to it's TI-Basic counterpart command, getkey. Getkey waits for a key press from the key pad. Then, depending on what you want to do, getkey can display the key code of the key pressed, execute another command, or act like a program pause.
This program will use _getkey as a program pause.
#define B_CALL(xxxx) rst 28h \ .dw xxxx
#define B_JUMP(xxxx) call 50h \ .dw xxxx
_clrlcdfull =4540h ;The ususal constants and defines, look at the
;New Commands section for more information
_homeup =4558h
_getkey =4972h
.org 9D95h
B_CALL(_homeup) ;Call up home screen
B_CALL(_getkey) ;Pause until next key press
B_CALL(_clrlcdfull) ;After key press, clear screen. Or you can use
;any other clear screen command (Tutorial 3)
ret ;Return to being a good old calculator
.end
END
_getkey - Detect key press, store key code if nessasary
We will make our own program that displays the Hex key code of the key pressed.The code for the program is here. It looks complicated, but it really isn't. I'll comment the program along the way so you don't get lost. An important concept is the "stack". The stack holds numbers for future use or reference. In this program, it holds the hex code of each key pressed.
#define B_CALL(xxxx) rst 28h \ .dw xxxx
#define B_JUMP(xxxx) call 50h \ .dw xxxx
_clrlcdf =4540h ;The ususal constants and defines, look at the
;New Commands section for more information
_homeup =4558h
_puts =450Ah
_putc =4504h
_getkey =4972h
_newline =452Eh
.org 9D95h
B_CALL(_clrlcdf) ; clear screen
B_CALL(_homeup) ; home the cursor
ld hl,txt1 ; Display the message at the txt1 label
B_CALL(_puts)
B_CALL(_getkey) ; Detect key press
push af ; Save key press in register a
B_CALL(_clrlcdf) ; clear screen again
B_CALL(_homeup) ; home again
ld hl,txt2 ; Display msg2
B_CALL(_puts) ; Display text
pop af ; restore reg a
call dishex ; Follow commands at label dishex to find hex key code
B_CALL(_getkey) ; pause until next key press
B_CALL(_newline) ; Move cursor to next line
ret ;Return to TI-OS
dishex: push af ; keep copy of value
and 0F0h ; terminate lower nibble
rra ; shift nibble right 4
rra
rra
rra
ld l,a ; Display the Key's hex code in Str1
ld h,0
ld de,hexStr
push de ; keep for other nibbler
add hl,de ; add offset to hexStr address
ld a,(hl) ; find correct ASCII character from string below to
; display hex code of key pressed.
bcall(_putc) ; display character
pop de
pop af
and 0Fh ; wipeout upper nibble
ld l,a
ld h,0
add hl,de
ld a,(hl)
bcall(_putc)
ret ; Return to OS
hexStr .db "0123456789ABCDEF" ;These are the characters used to display
;the key's hex code
txt1 .db "Push a key.",0
txt2 .db "Key code: ",0
.end
END
This program wasn't exactly "lightning fast". That's because the _Getkey command was scanning the entire key pad for a key press. Later on, we will make a program like this one, only we'll narrow down the area in which _Getkey looks in for a keypress, making it faster.
Tutorial 9