通過(guò)改變循環(huán)計(jì)數(shù)器LC[0]裝載的數(shù)值來(lái)改變輸出頻率(對(duì)應(yīng)于產(chǎn)生的音符)。通過(guò)改變循環(huán)計(jì)數(shù)器LC[1]裝載的數(shù)值來(lái)改變音符持續(xù)時(shí)間。把這些代碼打包到一個(gè)簡(jiǎn)單宏中，定義幾個(gè)常數(shù)，就很容易產(chǎn)生播放一小段音樂(lè)的代碼。

#define NOTE_C     261#define NOTE_C_SH  277#define NOTE_D_FL  277#define NOTE_D     294#define NOTE_D_SH  311#define NOTE_E_FL  311#define NOTE_E     330#define NOTE_F     349#define NOTE_F_SH  370#define NOTE_G_FL  370#define NOTE_G     392#define EIGHTH     1       ; 120 beats per minute, 4/4 time#define QUARTER    2       ; 120 beats per minute, 4/4 time#define QUARTERDOT 3       ; 120 beats per minute, 4/4 time#define HALF       4       ; 120 beats per minute, 4/4 time#define WHOLE      8       ; 120 beats per minute, 4/4 timeplay macro note, durationlocal L1, L2move    HRNC,  #1move    LC[1], #(note * duration / 8)L1:move    PO0.0, #1         ; Switch output high.move    LC[0], #(1785000 / note)djnz    LC[0], $          ; Decrement and jump, if not zero, to current ;    instruction.move    PO0.0, #0         ; Switch output low.move    LC[0], #(1785000 / note)djnz    LC[0], $          ; Decrement and jump, if not zero, to current ;    instruction.djnz    LC[1], L1         ; Decrement and jump, if not zero, to top of loop.move    HRNC,  #1move    LC[1], #50        ; 50ms of silenceL2:move    LC[0], #3570      ; 1ms (inner loop)  djnz    LC[0], $djnz    LC[1], L2endm
				
            

				
					
					
				
			
                
			
							

                
			            

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