https://7800.8bitdev.org/index.php?action=history&feed=atom&title=YM2151_Detection 2026-05-16T17:31:46Z Revision history for this page on the wiki MediaWiki 1.28.0 https://7800.8bitdev.org/index.php?title=YM2151_Detection&diff=869&oldid=prev 2021-04-10T16:26:56Z

<p>Created page with &quot;&lt;pre&gt; YM2151ADDR EQU $460 YM2151DATA EQU $461 XMCNTRL EQU $470 LDA #$70 STA CTRL ;TURN OFF MARIA LDA #$84 ;enable YM STA XMCNTRL LDA #$00 TAX YMLP1: JSR WRITEYMAD...&quot;</p> <p><b>New page</b></p><div>&lt;pre&gt;<br /> YM2151ADDR EQU $460<br /> YM2151DATA EQU $461<br /> XMCNTRL EQU $470<br /> <br /> LDA #$70<br /> STA CTRL ;TURN OFF MARIA<br /> <br /> LDA #$84 ;enable YM<br /> STA XMCNTRL<br /> <br /> LDA #$00<br /> TAX<br /> YMLP1: JSR WRITEYMADDR<br /> STA YM2151DATA<br /> INX<br /> BNE YMLP1 <br /> <br /> LDX #$14 ;disable counter<br /> LDA #00<br /> JSR WRITEYMADDR<br /> <br /> LDX #$12 ;set counter<br /> LDA #252 <br /> JSR WRITEYMADDR<br /> <br /> LDX #$14 ;enable counter<br /> LDA #$2A<br /> JSR WRITEYMADDR<br /> <br /> ;TIMER IS NOW ACTIVE SO LETS COUNT WHILE WAITING FOR THE CLOCK TO OVERFLOW<br /> LDY #$02<br /> REPEAT: LDX #$00<br /> POLLFLAG: INX<br /> BEQ YMNOTFOUND ;timeout if no ym present <br /> LDA YM2151DATA ;read counter flag<br /> AND #$02<br /> BNE CHECKCOUNT<br /> JMP POLLFLAG<br /> <br /> WRITEYMADDR<br /> BIT YM2151DATA<br /> BMI WRITEYMADDR<br /> STX YM2151ADDR<br /> WRITEYMDATA<br /> BIT YM2151DATA<br /> BMI WRITEYMDATA<br /> STA YM2151DATA<br /> RTS<br /> <br /> CHECKCOUNT:<br /> DEY<br /> BEQ CHKCNT<br /> LDX #$14 ;RESET COUNTER FLAG<br /> LDA #$2A<br /> JSR WRITEYMADDR<br /> JMP REPEAT<br /> CHKCNT: <br /> CPX #$80 ;COUNT SHOULD BE $88, CHECK IT'S BETWEEN $80-$90<br /> BCC YMNOTFOUND ;COUNT &lt; $80<br /> CPX #$90<br /> BCS YMNOTFOUND ;COUND &gt;=$90<br /> <br /> YMFOUND:<br /> LDA #$40<br /> STA CTRL<br /> LDA #$D4 ;MAKE BACKGROUND GREEN<br /> STA $20<br /> <br /> YMFOUNDLP: JMP YMFOUNDLP<br /> <br /> YMNOTFOUND:<br /> LDA #$40<br /> STA CTRL<br /> LDA #$46 ;MAKE BACKGROUND RED<br /> STA $20<br /> YMNOTFOUNDLP: JMP YMNOTFOUNDLP<br /> &lt;/pre&gt;</div>

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