How to understand this?

 # include & lt; Reg51. H> 
# define u8 unsigned char 
# define under-16 unsigned int 

Sbit BEEP=P2 ^ 3; 

Void delay_ms (under-16 x)//millisecond delay function 
{under-16 I, j; 
for(i=0; ifor(j=0; j<115; J++); 
} 

//happy birthday note frequency table, different frequency is decided by different time delay to 
U8 code SONG_TONE []={212212190212159169212212190212142159212212106126159169190119119126159142159, 0}; 

//happy birthday beat table, decided to each note playing length 
9,3,12,12,12,24,9,3,12,12,12,24,9,3,12,12,12,12,12,9,3,12,12,12,24,0 u8 code SONG_LONG []={}; 

Void PlayMusic () 
{
Under-16 I=0, j, k; 
While (SONG_LONG [I]!=0 | | SONG_TONE [I]!=0) 
{//play each note, SONG_LONG to beat length 
for(j=0; j{
BEEP=~ BEEP; 
//SONG_TONE delay table determines the frequency of each note 
for(k=0; K} 
delay_ms(10); 
i++; 
} 
} 

Void main () 
{
PlayMusic (); Happy birthday//play 
while(1);//play after stop 
} 

CodePudding user response:

By controlling the P2 ^ 3 pin high time and frequency to control the output voice, similar to the output PWM control