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109 lines
1.9 KiB
NASM
109 lines
1.9 KiB
NASM
; kbd
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;
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; Control TI-84+'s keyboard.
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;
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; *** Constants ***
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.equ KBD_PORT 0x01
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; *** Code ***
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; Wait for a digit to be pressed and sets the A register to the value (0-9) of
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; that digit.
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;
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; This routine waits for a key to be pressed, but before that, it waits for
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; all keys to be de-pressed. It does that to ensure that two calls to
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; waitForKey only go through after two actual key presses (otherwise, the user
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; doesn't have enough time to de-press the button before the next waitForKey
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; routine registers the same key press as a second one).
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;
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; Sending 0xff to the port resets the keyboard, and then we have to send groups
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; we want to "listen" to, with a 0 in the group bit. Thus, to know if *any* key
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; is pressed, we send 0xff to reset the keypad, then 0x00 to select all groups,
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; if the result isn't 0xff, at least one key is pressed.
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kbdGetC:
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push bc
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; loop until a digit is pressed
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.loop:
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; When we check for digits, we go through all 3 groups containing them.
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; for each group, we load the digit we check for in B and then test the
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; bit for that key. If the bit is reset, our key is pressed. we can
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; jump to the end, copy B into A and return.
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; check group 2
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ld a, 0xfb
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call .get
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ld b, '3'
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bit 1, a
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jr z, .end
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ld b, '6'
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bit 2, a
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jr z, .end
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ld b, '9'
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bit 3, a
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jr z, .end
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ld a, 0xf7
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call .get
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ld b, '2'
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bit 1, a
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jr z, .end
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ld b, '5'
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bit 2, a
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jr z, .end
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ld b, '8'
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bit 3, a
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jr z, .end
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; check group 4
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ld a, 0xef
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call .get
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ld b, '0'
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bit 0, a
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jr z, .end
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ld b, '1'
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bit 1, a
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jr z, .end
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ld b, '4'
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bit 2, a
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jr z, .end
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ld b, '7'
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bit 3, a
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jr z, .end
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jr .loop ; nothing happened? loop
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.end:
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; loop until all keys are de-pressed
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.loop2:
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xor a
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call .get
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inc a ; if a was 0xff, will become 0 (nz test)
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jr nz, .loop2 ; non-zero? something is pressed
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; copy result into A
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ld a, b
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pop bc
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ret
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.get:
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ex af, af'
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ld a, 0xff
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di
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out (KBD_PORT), a
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ex af, af'
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out (KBD_PORT), a
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in a, (KBD_PORT)
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ei
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ret
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