The base bit (CY) and data move left and right

2. Code
3. Summary

 

  Code
 
#include
sbit led=P2^0;
sbit led2=P2^1;
void DelayUs2x(unsigned char t)
{   
 while(--t);
}
void DelayMs(unsigned char t)
{
     
 while(t--)
 {
     //roughly delay 1mS
     DelayUs2x(245);
DelayUs2x(245);
 }
}
/*The following function is the essence of reverse scanning*/
unsigned char jpsm() //Matrix keyboard reverse scanning
{
unsigned char i=0; //Used to receive key value 
P0 = 0x0f; //Detect the lower 4 bits
if(0x0f != P0) //Detect whether the key is pressed
{
DelayMs(10); //Debounce
if(0x0f != P0) //Judge whether the key is really pressed instead of other interference
{
i = P0; //Assign the lower 4 bits to i
P0 = 0xf0; //Check the upper 4 bits
DelayUs2x(5); //Slight delay. This statement can be removed
i = i | P0; //Combine the lower 4 bits and the upper 4 bits into a complete key value
while( 0xf0 != P0 ) //Check if the key is released
{
;
}
return i; //Return the key value
}
}
return 0; //Return 0 if the key is not pressed
}

void main()
{
unsigned char i=0xaa;
while(1)
{
if(126 ==jpsm()) //Judge whether button 1 is pressed
{
/*i <<= 1; //Note: In the Keil compiler, no matter whether it is left shift or right shift, the shifted data is placed in CY
led = CY;*/
i >>=1;
led = CY;
        }
}  
}

Summary
1. What is a carry digit?
    Answer: It is used to store the carry digit.