When I was learning about C51 LED running lights, I wrote a piece of code. There was a sentence in the code that the software did not execute and was skipped directly.

Tacking

When I was learning about C51 LED running lights, I wrote a piece of code. There was a sentence in the code that the software did not execute and was skipped directly. [Copy link]

 

#include <REGX52.H>

unsigned char LEDNum; //define an unsigned character variable LEDNum

/*Define an unsigned integer n, which can set any delay time, based on the multiple of 1ms delay*/
void Delay(unsigned int n) //@12.000MHz
{
unsigned char i, j;

while(n--)
{
i = 2;
j = 239;
do
{
while (--j);
} while (--i);
}
}

/*Main function*/
void main()
{
LEDNum=0x01;
while(1)
{
if(LEDNum>=0x81)
LEDNum=0x01;
else
{
LEDNum<<1;
P2=~LEDNum;
Delay(500);
}
}
}

The original intention is: define an unsigned character LEDNum, initially assign a value of 0000 0001, and then judge by the conditional statement. If LEDNum is greater than 1000 0001, reassign it to 0000 0001. If it is less than 1000 0001, execute LEDNum<<1 and shift it left by one bit. However, I found that this sentence was ignored when I executed it in a single step, and it was not executed, so the final result was not right. I would like to ask experts to help point out the cause of the problem. I am a novice and I am very grateful.

dcexpert

It has been optimized by the compiler and can be executed by turning off optimization.

damiaa

LEDNum<<=1;

秦天qintian0303

Add a breakpoint and try it. It shouldn't fail to execute.

Tacking

Thank you, I found the problem. It should be written as: LEDNum=LEDNum<<1; LEDNum is just shifted left by one position. If LEDNum is not reassigned after the left shift, the value of LEDNum will remain unchanged, so it is optimized. After changing it to an assignment statement, there is no problem and it can be executed. Thank you very much

hellokitty_bean

Accumulate experience...Continue to improve!!!

suiyue9528

If the unsigned LEDNum=0x01 is shifted left, the maximum value is 0x80. How can it be greater than or equal to 0x81? This is where the problem lies. When it reaches 0x80, the next shift left is 0, so the final LEDNum is always 0

Tacking

suiyue9528 posted on 2024-5-21 10:30 Unsigned LEDNum=0x01 keeps shifting left, the maximum value is 0x80, how can it be greater than or equal to 0x81? This is the problem. When it reaches 0x80, shift left again...

Thank you very much, it really enlightened me! I will correct it later.

Tacking

suiyue9528 posted on 2024-5-21 10:30 Unsigned LEDNum=0x01 keeps shifting left, the maximum value is 0x80, how can it be greater than or equal to 0x81? This is the problem. When it reaches 0x80, shift left again...

When I was learning the code for key-controlled LED on and off today, I used the if...else... statement. The code is as follows:

void main()
{
while(1)
{
if(P3_0==0)
{
Delay(20);
while(P3_0==0);
Delay(20);
P2_0=~P2_0;
}
// else
// P2_0=P2_0 ;
}
}

When executing, I found that when adding the last else statement, the button cannot control the LED on and off, and the state of P2_0 remains unchanged. On the contrary, when removing the else statement, it becomes normal! Please guide me, why is this? Shouldn't there be an else statement after if?

Tacking

Tacking posted on 2024-5-21 17:59 Today, when I was learning the code for key-controlled LED on and off, I used the if...else... statement. The code is as follows: void main() { ...

Please let me know if you understand this issue. Thank you very much

emma2015

If the unsigned LEDNum=0x01 is shifted left, the maximum value is 0x80. How can it be greater than or equal to 0x81? This is where the problem lies. When it reaches 0x80, the next shift left is 0, so the final LEDNum is always 0

damiaa

Tacking posted on 2024-5-21 09:39 Thank you, I found the problem. It should be written as: LEDNum=LEDNum<<1; LEDNum is just shifted left by one bit, and LEDNum is not reassigned after the left shift...

LEDNum<<=1; LEDNum=LEDNum<<1; should be the same. Try it.

suiyue9528

Tacking posted on 2024-5-22 09:52 Please let me know if you understand this issue, thank you very much

When the state of P3_0 is 1, P2_0=P2_0 will be executed. Here, change it to P2_0=~P2_0 to reverse the level.

Tacking

damiaa posted on 2024-5-22 13:01 LEDNum<<=1; LEDNum=LEDNum<<1; should be the same. You try it.

LEDNum<<=1 is the same as LED=LEDNum<<1. I wrote LEDNum<<1 before without adding "=". When compiling, this sentence was always optimized away by the program and not executed. I changed it to LEDNum<<=1 and it worked. I've learned a lot. Thank you very much. It turned out that I had a syntax error.

Tacking

suiyue9528 posted on 2024-5-23 09:51 When the state of P3_0 is 1, P2_0=P2_0 will be executed. Here, change it to P2_0=~P2_0, and the level can be reversed

The idea of my code is that when the state of P3_0 is 1, the state of P2_0 remains unchanged, and when the state of P3_0 is 0, the state of P2_0 flips. The execution result shows that after adding the else statement, the state cannot be flipped, and P2_0 keeps the same state. After removing the else statement, it can flip normally.