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49 lines
3.8 KiB
Plaintext
49 lines
3.8 KiB
Plaintext
0000- 4 ;
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0000- 5 ; FROM THE BOOK '6502 GAMES', EXPECTS THE SAME HARDWARE AS DECRIBED WITHIN IT.
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0000- 6 ; THIS PART WAS NOT MEANT TO BE RUN DIRECTLY, SO I'VE JUST KEPT THE ADDRESS
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0000- 7 ; DEFINITIONS GIVEN IN THAT CHAPTER.
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0000- 8 ;
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C000- 9 VIA1 .EQ $C000
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CC00- 10 VIA3 .EQ $CC00
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0000- 11
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0100- 12 .OR $0100 ; NOTE: BOOK PLACES $0100 INSIDE STACK, MEANING
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0100- 13 .TA $0100 ; THAT ROUTINE MAY EASILY GET OVERWRITTEN.
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0100- 14 .IN getkey_routine.asm
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0100- I 1 ; 'GETKEY' KEYBOARD INPUT ROUTINE READS AND DEBOUNCES KEYBOARD. RETURNS WITH
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0100- I 2 ; KEY NUMBER IN ACCUMULATOR IF KEY DOWN. OPERATION: SENDS NUMBERS 0-F TO 74154
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0100- I 3 ; (4 TO 16 LINE DECODER), WHICH GROUNDS ONE SIDE OF KEYSWITCHES ONE AT A TIME.
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0100- I 4 ; IF A KEY IS DOWN, PA7 OF VIA #3 WILL BE GROUNDED, AND THE CURRENT VALUE
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0100- I 5 ; APPLIED TO THE 74154 BE THE KEY NUMBER. WHEN THE PROGRAM DETECTS A KEY CLOSE
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0100- I 6 ; CHECKS FOR KEY CLOSURE FOR 50 MS. TO ELIMINATE BOUNCE.
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0100- I 7 ; NOTE: IF NO KEY IS PRESSED, GETKEY WILL WAIT.
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0100- I 8 ;
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CC03- I 9 DDR3A .EQ VIA3+3 ; USING RC-ONE ADDRESS DECODING SCHEME, PLACING
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CC02- I 10 DDR3B .EQ VIA3+2 ; VIA3 AT $CC00 BY DEFAULT (INSTEAD OF $AC00)
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CC01- I 11 PORT3A .EQ VIA3+1 ; TO FIT RC-ONE ADDRESS DECODING THOUGH ORIGINAL
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CC00- I 12 PORT3B .EQ VIA3 ; CAN BE JUMPERED IF NEEDED/WANTED.
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0100- I 13
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0100-A9 00 I 14 ( 2) LDA #0
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0102-8D 03 CC I 15 ( 4) STA DDR3A ; SET KEY STROBE PORT FOR INPUT
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0105-A9 FF I 16 ( 2) LDA #$FF
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0107-8D 02 CC I 17 ( 4) STA DDR3B ; SET KEYS FOR OUTPUT
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010A-2C 01 CC I 18 ( 4) GETKEY BIT PORT3A ; SEE IF KEY IS STILL DOWN FROM LAST KEY CLOSURE:
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010D- I 19 ; KEYSTROBE IN 'N' STATUS BIT.
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010D-10 FB I 20 (2**) BPL GETKEY ; IF YES, WAIT FOR KEY RELEASE
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010F-A2 0F I 21 ( 2) RSTART LDX #15 ; SET KEY COUNTER TO 15
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0111-8E 00 CC I 22 ( 4) NXTKEY STX PORT3B ; OUTPUT KEY # TO 74154
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0114-2C 01 CC I 23 ( 4) BIT PORT3A ; SEE IF KEY DOWN: STROBE IN 'N'
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0117-10 05 I 24 (2**) BPL BOUNCE ; IF YES, GO DEBOUNCE
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0119-CA I 25 ( 2) DEX ; DECREMENT KEY #
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011A-10 F5 I 26 (2**) BPL NXTKEY ; NO, DO NEXT KEY
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011C-30 F1 I 27 (2**) BMI RSTART ; START OVER
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011E-8A I 28 ( 2) BOUNCE TXA ; SAVE KEY NUMBER IN A
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011F-A0 12 I 29 ( 2) LDY #$12 ; OUTER LOOP CNT LOAD FOR DELAY OF 50 MS.
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0121-A2 FF I 30 ( 2) LP1 LDX #$FF ; INNER 11 US. LOOP
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0123-2C 01 CC I 31 ( 4) LP2 BIT PORT3A ; SEE IF KEY STILL DOWN
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0126-30 E7 I 32 (2**) BMI RSTART ; IF NOT, KEY NOT VALID, RESTART
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0128-CA I 33 ( 2) DEX
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0129-D0 F8 I 34 (2**) BNE LP2 ; THIS LOOP USES 2115*5 US.
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012B-88 I 35 ( 2) DEY
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012C-D0 F3 I 36 (2**) BNE LP1 ; OUTER LOOP: TOTAL IS 50 MS.
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012E-60 I 37 ( 6) RTS ; DONE: KEY IN A.
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