68 lines
1.7 KiB
NASM
68 lines
1.7 KiB
NASM
.CR 6502
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.TF piano.hex,INT
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.LF piano.list
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* ----------------------------------------------------------------------
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* PLAY A SINGLE NOTE USING TIMER1 ON 6522 (VIA) FOUND ON THE PROJECT
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* BOARD. REQUIRES INTERRUPT VECTOR CONFIGURED TO POINT TO INTR (SEE
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* LISTING).
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*
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VOLUME .EQ $D0
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TEMP .EQ $D1
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OUTPUT .EQ $D2
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POINTH .EQ $FB DIGITS 1-2
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POINTL .EQ $FA DIGITS 3-4
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INH .EQ $F9 DIGITS 5-6
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SCANDS .EQ $1F1F
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VIA .EQ $1700
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IRB .EQ VIA
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ORA .EQ VIA + $1
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DDRB .EQ VIA + $2
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DDRA .EQ VIA + $3
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T1CL .EQ VIA + $4
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T1CH .EQ VIA + $5
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ACR .EQ VIA + $B
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IER .EQ VIA + $E
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.OR $0200
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.TA $0200
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SETUP LDA #$FF SET PORT A
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STA DDRA AS OUTPUTS
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LDA #$00 SET PORT B
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STA DDRB AS INPUTS
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TIMER LDA #$FF RESET TIMER1
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STA T1CL
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STA T1CH
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LDA #$40 FREE-RUN MODE WITHOUT
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STA ACR ENABLING OUTPUT ON PB7
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LDA #$C0 ENABLE VIA
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STA IER INTERRUPT
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CLI ENABLE CPU INTERRUPT
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WAIT LDA #$FF READ SWITCHES,
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EOR IRB BUT INVERT LOGIC
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STA VOLUME TO AVOID KEEPING
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JMP WAIT VOLUME AT 100%
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SETNOTE LDA #$E4
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STA T1CL
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LDA #$17
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STA T1CH
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RTS
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INTR LDA T1CL
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LDA VOLUME
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CMP TEMP
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BEQ TOGGLE
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STA TEMP
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STA OUTPUT
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TOGGLE LDA #$FF
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EOR OUTPUT
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STA OUTPUT
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STA ORA
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CLI
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RTI |