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Help needed! PWM speed increases but does not decreses

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0killingsoul0

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I am trying to make a pwm using 8051. I am using external interrupt 0 (pin 3.1) to increase speed and interrupt 1 (pin 3.2) to decrease speed. My code is working fine for increasing speed but it does not work for decreasing speed. i.e interrupt 1 is not working properly.

Capture.PNG:**broken link removed**

**broken link removed**

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Code C - [expand]
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#include<reg51.h>
 
 
 
 
unsigned char inc = 0;
 
void MSDelay(unsigned int);
void ex0_isr (void) interrupt 0
{
inc++;   // Increment the count
}
 
 
void ex1_isr (void) interrupt 1
{
inc=inc--;   // Deccrement the count
}
 
 
 
sbit pwm=P2^0;
sbit pwmn=P2^1;
sbit enable=P2^2;
 
 
 
 
 
void universal_delay(unsigned int);
 
void main( )
{     IT0 = 1;   // Configure interrupt 0 for falling edge on /INT0 (P3.2)
      IT1 = 1;   // Configure interrupt 1 for falling edge on /INT0 (P3.2)
      
      
      EX0 = 1;   // Enable EX0 Interrupt
      EX1 = 1;
      
      EA = 1;    // Enable Global Interrupt Flag
     
     enable=1;          
     
     pwm=0;       //  making outputs
     pwmn=0;
 
 
 
    
 
    while(1)
    {     
        universal_delay(inc);
    }
 
}
 
 
 
void universal_delay(unsigned int d)
{
            if (d==1)
            {   
                
                pwm=1;
                pwmn=0;
                
                MSDelay(50);      //  50 ms delay
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(50);
                
            
            }
 
        else if (d== 2)
        
        {   
             pwm=1;
                pwmn=0;
                
                MSDelay(55);
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(45);    
                    
            }
 
 
        else if (d== 3)
            {   
                 pwm=1;
                pwmn=0;
                
                MSDelay(60);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(40);
        }
 
        
        else if (d==4)
            {    
                                pwm=1;
                pwmn=0;
                
                MSDelay(65);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(35);
            }
 
            else if (d==5)
        
            {    pwm=1;
                pwmn=0;
                
                MSDelay(70);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(30);
            
            }
 
        else if (d== 6)
        
            {   
                 pwm=1;
                pwmn=0;
                
                MSDelay(75);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(30);
            }
 
        else if (d== 7)
              {
                 pwm=1;
                pwmn=0;
                
                MSDelay(75);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(25);
                }
 
                    else if (d== 8)
              {
                 pwm=1;
                pwmn=0;
                
                MSDelay(80);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(20);
                }
 
                else if (d== 9)
              {
                 pwm=1;
                pwmn=0;
                
                MSDelay(85);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(15);
                }
                else if (d== 10)
              {
                 pwm=1;
                pwmn=0;
                
                MSDelay(90);    
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(10);
                }
        
 
                    else if (d>10)
              {
                 pwm=1;
                pwmn=0;
                               
                MSDelay(100);   
                    
                pwm=0;
                pwmn=1;
 
                MSDelay(0);
                }
 
 
        
    
}
 
 
 
void MSDelay(unsigned int itime)
{
unsigned int i,j;
for (i=0;i<itime;i++)
for (j=0;j<1275;j++);
}
 
Last edited:

I have never used 8051 mcu so I may not be of much help but one thing I see is that the inc variable is not decalerd as volatile and you should always do that when you have a variable used in both main and isr and may be changed in isr.

You have also used inc = inc-- in isr1 , this should have the same result as inc-- so why don't you just use inc--.

Maybe you also want to use some kind of condition so that the variable doesn't go below 0 (which will result in 255), for example
Code: 
if (inc>0)	inc--; // Decrement the count
maybe you should apply that in isr0too
Code: 
if (inc<255)	inc++; // increment the count

I'm not sure why your code strucks where it does.

Alex
 

Thanks for the reply. Tired of removing this glitch but still no success :( .

I don't know why the second interrupt 1 is not working properly. As i have showed in the picture. That interrupt is not returning properly.

3.PNG
 

What compiler do you use?

I didn't worked in past period with 8051 devices, but I remember that you should specify also interrupt attribute (interrupt vector). Try the following code:

Code C - [expand]
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void ex0_isr (void) interrupt 0 using 0
{
inc++;   // Increment the count
}
 
 
void ex1_isr (void) interrupt 1 using 2
{
inc=inc--;   // Deccrement the count
}

Example how to define interrupts in Keil
 
Last edited by a moderator:

cristianp said:
What compiler do you use?

I didn't worked in past period with 8051 devices, but I remember that you should specify also interrupt attribute (interrupt vector). Try the following code:

Code C - [expand]
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void ex0_isr (void) interrupt 0 using 0
{
inc++;   // Increment the count
}
 
 
void ex1_isr (void) interrupt 1 using 2
{
inc=inc--;   // Deccrement the count
}

Example how to define interrupts in Keil
Click to expand...



Tried this but still no success..... :(.
 

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