Well yes the problem is one of getting stuck at the four points as mentioned by me. I did try out a trick like this :

- Configure the Timer 2 for a 10mS time out.
- Start the Timer2 first thing after the 100mS delay function.
- Stop Timer2 as the last event before exiting the While(1) loop.
- And inside Timer2 ISR, have a counter increment for every call. If the counter reaches 5 ( =50mS), reset the display to Zero. And also reset the Counter.

//----------------------------------------------

/* Timer_2 is used as the timeout timer for the 
software multiplexed display. It is set to run
at 10ms interval and if there is no pulse for 
this (duration x 5 = 50mS ) clear`the display..*/

void timer2_int(void) interrupt 5
{
  ++timeOut;
  TF2 = 0; 
  
  if (timeOut == 5)
     {
      tmpResult = 0;
      sprintf(dispBuffer, "%04lu", tmpResult );
      timeOut = 0;
     }
}

//-----------------------------------------------

This logic works most times, but there is this occasional "0" reading even when the rpm is in the valid range. Maybe there is a flaw somewhere in the logic or implementation..

My minimum speed range is well above 100 rpm.

Is there any other elegant way ?

Thanks for your time.

Raghu