The principle of music programming based on single chip microcomputer

    Using a single-chip microcomputer (or single-board computer) to play music is probably one of the issues that radio enthusiasts are interested in. This article starts with the basic experiment of single-chip microcomputers, discusses the design principles of music programs, and gives specific examples for reference.

    Basic pronunciation experiment of single chip microcomputer

    We know that the frequency spectrum of sound ranges from about tens to thousands of hertz. If we can use a program to control the "high" or low level of a certain line of a single machine, a rectangular wave of a certain frequency can be generated on the line, and a speaker can emit a sound of a certain frequency. If we use a delay program to control the duration of the "high" and "low" levels, we can change the output frequency and thus change the tone.

    For example, to generate a 200Hz audio signal, connect the speaker as shown in Figure 1 (if it is a temporary experiment, the speaker can also be directly connected to the P1 port line). The experimental procedure is:

    Among them, subroutine DEL is a delay subroutine. When R3 is 1, the delay time is about 20us. R3 stores the delay constant. For 200HZ audio, its period is 1/200 second, that is, 5ms. In this way, when the duration of the high or low level of P1.4 is 2.5ms, that is, when the time constant of R3 is 2500/20=125 (7DH), a 200HZ tone can be emitted. Type the above program into the learning machine, and continuously modify the constant of R3 to feel the change of tone. In the music, each note corresponds to a certain frequency. Table 1 gives the frequency of each note in C key and its corresponding time constant. Readers can send its hexadecimal code into R3 according to the constants provided in Table 1, and practice repeatedly to experience it. According to Table 1, notes can be played. This is not enough. To play a song accurately, the rhythm of the music must be accurately controlled, that is, the duration of a note.

    We can use timer T0 to control the beat of the note. By inputting different initial values, we can generate different timing times. For example, the rhythm of a song is 94 beats per minute, that is, one beat is 0.64 seconds. The corresponding relationship between other beats and time is shown in Table 2.

    However, since the maximum timing time of T0 can only be 131 milliseconds, it is impossible to directly change the initial value of T0 to achieve different beats. We can use T0 to generate a 10 millisecond time base, and then set an interrupt counter to control the length of the beat time by judging the value of the interrupt counter. Table 2 also gives the time constants corresponding to various beats. For example, for a 1/4 beat note, the timing time is 0.16 seconds, and the corresponding time constant is 16 (ie 10H); for a 3-beat note, the timing time is 1.92 seconds, and the corresponding time constant is 192 (ie C0H).

    We take the time constant of each note and its corresponding beat constant as a group, arrange all the constants in the music into a table in order, and then use the table lookup program to take them out in turn, generate notes and control the rhythm, so that the performance effect can be achieved. In addition, the end note and the body stop note can be represented by the codes 00H and FFH respectively. If the table lookup result is 00H, it means the end of the song; if the table lookup result is FFH, the corresponding pause effect is generated. In order to produce the rhythm of hand playing, some notes (such as two identical notes) are inserted with a slightly different frequency of one time unit.

    The following is a program list that can be played directly on the TD-III learning machine. For other different models of learning machines, just change the address accordingly. This program plays the folk song "Osmanthus flowers bloom everywhere in August", in the key of C, with a rhythm of 94 beats per minute. Readers can also find a song by themselves, translate the music into a code table according to the constants given in Tables 1 and 2, and input it into the machine without changing the program. This experimental method is simple. Even for people who don't understand music, it is easy to translate an unfamiliar song into code. Learning to sing a song along with the performance of the machine is endless fun.

    Program listing (omitted, please refer to the source program description).

    The program flowchart is shown in Figure 2.

    This course is provided by the MCU Tutorial Network. Please point out any problems.

    Hardware connection instructions:

    Just find a simulator or a microcontroller experiment board, as long as it works, input the program, run it, then find a speaker (there should be a pair next to your computer), unplug it, connect the front end of the plug to P1.0, and find a wire to connect the back part to the ground of the microcontroller, and there should be sound. Then it is up to you to improve the hardware connection...

    Music program assembly code Code 1 -------------VoICe.asm--------------------------

            ORG 0000H
        LJMP START
        ORG 000BH
        INC 20H ;Interrupt service, interrupt counter plus 1
        MOV TH0,#0D8H
        MOV TL0,#0EFH ;12M crystal, forming a 10 millisecond interrupt
        RETI
START:  
        MOV SP,#50H
        MOV TH0,#0D8H
        MOV TL0,#0EFH
        MOV TMOD,#01H
        MOV IE,#82H
MUSIC0:
        NOP
        MOV DPTR,#DAT ;Table header address sent to DPTR
        MOV 20H,#00H ;Interrupt counter cleared to 0
        MOV B,#00H ;Table number cleared to 0
MUSIC1:
        NOP
        CLR A
        MOVC A,@A+DPTR ;Look up the table to get the code
        JZ END0 ;If it is 00H, then end
        CJNE A,#0FFH,MUSIC5
        LJMP MUSIC3
MUSIC5:
        NOP
        MOV R6,A
        INC DPTR
        MOV A,B
        MOVC A,@A+DPTR ;Get the beat code and send it to R7
        MOV R7,A
        SETB TR0 ;Start counting
MUSIC2:
        NOP
        CPL P1.0
        MOV A,R6
        MOV R3,A
        LCALL DEL
        MOV A,R7
        CJNE A,20H,MUSIC2 ;Is the interrupt counter (20H) = R7?
                                ;If not equal, continue the loop
        MOV 20H,#00H ;If equal, get the next code
        INC DPTR
; INC B
        LJMP MUSIC1
MUSIC3:
        NOP
        CLR TR0 ;Pause for 100 milliseconds
        MOV R2,#0DH
MUSIC4:
        NOP
        MOV R3,#0FFH
        LCALL DEL
        DJNZ R2,MUSIC4
        INC DPTR
        LJMP MUSIC1
END0:
        NOP
        MOV R2,#64H ;Song ends, delay 1 second and continue
MUSIC6:
        MOV R3,#00H
        LCALL DEL
        DJNZ R2,MUSIC6
        LJMP MUSIC0
DEL:
        NOP
DEL3:                  
        MOV R4,#02H
DEL4:   
        NOP
        DJNZ R4,DEL4
        NOP
        DJNZ R3,DEL3
        RET
        NOP

DAT:
 db 26h,20h,20h,20h,20h,20h,26h,10h,20h,10h,20h,80h,26h,20h,30h,20h
 db 30h,20h,39h,10h,30h,10h,30h,80h ,26h,20h,20h,20h,20h,20h,1ch,20h
 db 20h,80h,2bh,20h,26h,20h,20h,20h,2bh,10h,26h,10h,2bh,80h,26h,20h
 db 30h,20h,30h,20h,39h,10h,26h,10h,26h,60h,40h,10h,39h,10h,26h,20h
 db 30h,20h,30h,20h,39h,10h,26h,10h,26h, 80h,26h,20h,2bh,10h,2bh,10h
 db 2bh,20h,30h,10h,39h,10h,26h,10h,2bh,10h,2bh,20h,2bh,40h,40h,20h
 db 20h,10h,20h,10h,2bh,10h,26h,30h,30h,80h,18h,20h,18h,20h,26h,20h
 db 20h,20h,20h,40h,26h,20h,2bh,20h,30h, 20h,30h,20h,1ch,20h,20h,20h
 db 20h,80h,1ch,20h,1ch,20h,1ch,20h,30h,20h,30h,60h,39h,10h,30h,10h
 db 20h,20h,2bh,10h,26h,10h,2bh,10h,26h,10h,26h,10h,2bh,10h,2bh,80h
 db 18h,20h,18h,20h,26h,20h,20h,20h,20h, 60h,26h,10h,2bh,20h,30h,20h
 db 30h,20h,1ch,20h,20h,20h,20h,80h,26h,20h,30h,10h,30h,10h,30h,20h
 db 39h,20h,26h,10h,2bh,10h,2bh,20h,2bh,40h,40h,10h,40h,10h,20h,10h
 db 20h,10h,2bh,10h,26h,30h,30h,80h,00H

    END

    Music program assembly code Code 2 -------------Vo IC e1.asm--------------------------

    ;Title 'August Osmanthus Fragrance' Voice Program        
;Abstract For details, see 'Radio' Issue 3, 1992
;Author Zhou ZhenanORG
  0000H
        LJMP START
        ORG 000BH
        INC 20H ;Interrupt service, interrupt counter plus 1
        MOV TH0,#0D8H
        MOV TL0,#0EFH ;12M crystal oscillator , forming a 10 millisecond interrupt
        RETI
START:  
        MOV SP,#50H
        MOV TH0 ,#0D8H MOV
        TL0,#0EFH
        MOV TMOD,#01H
        MOV IE,#82H
MUSIC0:
        NOP
        MOV DPTR,#DAT ;Table header address sent to DPTR
        MOV 20H,#00H ;Interrupt counter cleared to 0
        MOV B,#00H ;Table number cleared to 0
MUSIC1:
        NOP
        CLR A
        MOVC A,@A+DPTR ;Look up the table to get the code
        JZ END0 ;If it is 00H, then end
        CJNE A,#0FFH,MUSIC5
        LJMP MUSIC3
MUSIC5:
        NOP
        MOV R6,A
        INC DPTR
        MOV A,B
        MOVC A,@A+DPTR ;Get the beat code and send it to R7
        MOV R7,A
        SETB TR0 ;Start counting
MUSIC2:
        NOP
        CPL P1.0
        MOV A,R6
        MOV R3,A
        LCALL DEL
        MOV A,R7
        CJNE A,20H,MUSIC2 ;Is the interrupt counter (20H) = R7?
                                ;If not equal, continue the loop
        MOV 20H,#00H ;If equal, then get the next code
        INC DPTR
; INC B
        LJMP MUSIC1
MUSIC3:
        NOP
        CLR TR0 ;Pause for 100 milliseconds
        MOV R2,#0DH
MUSIC4:
        NOP
        MOV R3,#0FFH
        LCALL DEL
        DJNZ R2,MUSIC4
        INC DPTR
        LJMP MUSIC1
END0:
        NOP
        MOV R2,#64H ;Song ends, delay 1 second and continue
MUSIC6:
        MOV R3,#00H
        LCALL DEL
        DJNZ R2,MUSIC6
        LJMP MUSIC0
DEL:
        NOP
DEL3:                  
        MOV R4,#02H
DEL4:   
        NOP
        DJNZ R4,DEL4
        NOP
        DJNZ R3,DEL3
        RET
        NOP

DAT:   
        DB 18H, 30H, 1CH, 10H
        DB 20H, 40H, 1CH, 10H     
        DB 18H, 10H, 20H, 10H
        DB 1CH, 10H, 18H, 40H
        DB 1CH, 20H, 20H, 20H
        DB 1CH, 20H, 18H, 20 H     
        DB 20H, 80H, 0FFH, 20H
        DB 30H, 1CH, 10H, 18H
        DB 20H, 15H, 20H, 1CH
        DB 20H, 20H, 20H, 26H
        DB 40H, 20H, 20H, 2BH
        DB 20H, 26H, 20 H , 20H     
        DB 20H, 30H, 80H, 0FFH
        DB 20H, 20H, 1CH, 10H
        DB 18H, 10H, 20H, 20H
        DB 26H, 20H, 2BH, 20H
        DB 30H, 20H, 2BH, 40H
        DB 20H, 20H, 1CH, 10H
        DB 18H, 10H, 20H, 20H
        DB 26H, 20H, 2BH, 20H
        DB 30H, 20H, 2BH, 40H
        DB 20H, 30H, 1CH, 10H
        DB 18H, 20H, 15H, 20H
        DB 1CH, 20H, 20H , 20H
        DB 26H, 40H, 20H , 20H     
        DB 2BH, 20H, 26H , 20H     
        DB 20H, 20H, 30H , 80H
        DB 20H, 30H, 1CH , 10H
        DB 20H, 10H, 1CH , 10H
        DB 20H, 2 0H, 26H, 20H
        DB 2BH, 20H, 30H, 20H
        DB 2BH, 40H, 20H, 15H
        DB 1FH, 05H, 20H, 10H
        DB 1CH, 10H, 20H, 20H
        DB 26H, 20H, 2BH, 20H
        DB 30H, 20H, 2BH, 40H
        DB 20H, 30H, 1CH, 10H
        DB 18H, 20H, 15H, 20H
        DB 1CH, 20H, 20H, 20H
        DB 26H, 40H, 20H, 20H
        DB 2BH, 20H, 26H, 20H
        DB 20H, 20H, 30H, 30H      
        DB 20H, 30H, 1CH, 10H
        DB 18H, 40H, 1CH, 20H
        DB 20H, 20H, 26H, 40H
        DB 13H, 60H, 18H, 20H
        DB 15H, 40H, 13H, 40H
        DB 18H, 80H, 00H
end