Variable Delay (controlled with push switches)

Hi, I am using the 8051 to create a delay function with a variable (in this case BPMtime). At first the BPMtime variable is set to 100 and when i push and release the switch (on P0.0), the BPMtime becomes 101 hence the delay is increased. The same goes for the switch on P0.1 but instead of incrementing by one, i would like it to be decremented by one.

To know if it is working correctly, I outputted BPMtime to port 3 to see if the value is changed whenever i press one of the buttons. So far for some reason the program isn't working correctly. When one of the switches is pushed, the BPMtime stays 100. P0 doesn't have internal pull ups. The program is compiling successfully.

The program so far:

#include <reg51.h>

void BPMDelay();
unsigned char BPMtime;

void main(void)
{
P0=0xFF;
BPMtime=100;

while(1)
{
P2 = 0x00;
BPMDelay();
P2 = 0xFF;
BPMDelay();
}
}

void BPMDelay()
{
if (P0^0==0)
{
BPMtime=BPMtime ++;
P3=BPMtime;
}

if(P0^1==0)
{
BPMtime=BPMtime --;
P3=BPMtime;
}

else
{
unsigned int u,v;
for(u=0;u<BPMtime;u++);
for(v=0;v<190;v++);
}
}


Thanks for your time.

I wouldn't use XOR in this way.. P0^0 wont do anything write P0 & 1 and P0 & 2 for the key enquiry.

ie.. if(P0 & 1) blah blah ( you dont even need the equality part)

P0^0 and P0^1 refer to pins P0.0 and P0.1 respectively. i didnt exactly understood your reply. thanks

P0^0 means P0 xor 0 .. Is this what you want to acheive? I use and.. P0 & 1

im using keil as a compiler. in keil, P0^0 means P0.0

Ok! Then P0 = 0xff, not P0 = 0 you need P0 to be an input port!

unsigned int u,v;
for(u=0;u<BPMtime;u++);
for(v=0;v<190;v++);

Click to expand...

The compiler is probably optimizing the variables.
Try declaring them as volatile.
Like so:

volatile unsigned int u,v;

Ian Rogers said:

Ok! Then P0 = 0xff, not P0 = 0 you need P0 to be an input port!

Click to expand...

yes that was a mistake. i edit the program and put it in my first post. but still no luck with it working. Port 3 is still isplaying "100" (in binary of course)

ItsMike, I have declared them as volatile also but the program worked the same as it was...

10x

I've looked at the compiler P0^0 can also be written P0_0! does this make a difference.

Also try

if(P0 & 1)

and

if(P0 & 2)