Question

I am writing a very simple application which allows one to change the temperature. The temperature is displayed using LEDS (BCD format)

I wrote the following code in Keil C51:

#include< REG51.h>

sbit select = P1^7;
sbit up = P1^0;
sbit down = P1^1;
int data room = 24;

void main()
{   int prog;
    P2 &=0x00;
    P1 |=0x83;
    prog = 0;
    while (1)
    {
        if(select == 1)
            prog++;
        if(prog == 1)
        {
            if(up == 1)
                room++;
            if(down == 1)
                room--;

            P2 = room;
        }
    }
}

I then complied this and obtained the Intel hex file which i then tried to simulate using the Edsim.

According to the C code the temp should change when prog=1 and when either up(p1.0) or down(p1.1) is pressed, but in the simulation it only changes when both select(p1.7) and up/down is pressed!

Why is this happening?

Answer 1

prog++ means that the value of prog increments by 1 every time that the condition select == 1 is true. This means that the condition prog == 1 is true only on the first iteration that it’s incremented.

Try changing prog++ to prog = 1.

Edit: As per discussion in comments, if you wish to track the number of times select has gone up, you need to wait for it to be 0 again before you let prog be incremented again. For example:

int prev = select;
…
if (select != prev) {
    // select has changed from its previous state

    prev = select;
    if (prev) {
        // select went from 0 to 1
        ++prog;

        if (prog == 1) {
           // code to be executed once only on the first press
        } else if (prog == 2) {
           // code to be executed once only on the second press
        } else if (prog >= 3) {
           // code to be executed once on every subsequent press
        }
    } else {
        // select went from 1 to 0
    }
}

if (prev) {
   // select is being pressed

   if (prog == 1) {
       // code to be executed _continuously_ while select is held down
       // (after first press only)
   }
   // ...
}