RPM - DIV32 Problem

[davewanna]

ok I have done some more changes... just for debugging purposes... My code now looks like:

  PULSIN PORTD.6,1,rlow                             
  PULSIN PORTD.6,0,rhigh                            
  rtotal = (rlow + rhigh) / 10
  tbase = 500 * 600
  rpm = div32 280
  if rpm = 65535 then
    rpm = 0
  endif

This was to test if putting the variable rtotal after the DIV32 command was in any way incorrect. According to what I understand, it should now just display a fixed 1071rpm on the LCD.

However... when I now start the engine, at any rpm lower than roughly 1100 (probably 1071 to be precise), the display shows 0rpm, but over that, as I rev the engine, it shows RPM in the 32000 + range.

WHAT IS DIV32 DIVIDING BY 280??? Cause it's not 300000...

[mister_e]

seems we post at the same time

[davewanna]

Mister_e you are my hero!!

That was the problem, I wasn't using variables. I originally had it trying to divide by 3,000,000 but thought I might be over-flowing for some reason, and tried it at 300,000.

DIV32 was taking the last calculation using variables (rlow + rhigh /10) and therefore dividing rtotal by itself.. which was giving me a 1 while running, and a 0 while off...

All makes sense now really..

Just for interests sake, code now looks like

a = 50
b = 60000
...
  PULSIN PORTD.6,1,rlow                             
  PULSIN PORTD.6,0,rhigh                            
  rtotal = rlow + rhigh
  tbase = a * b
  rpm = div32 rtotal
  if rpm = 65535 then
    rpm = 0
  endif

Thankyou very much, many hours were wasted over that.

Now that I have it conquered, I will learn more about timers and interrupts.

[mister_e]

I knew there was a "fussy" code writing thing in that. Better explanation at the following link
http://www.picbasic.co.uk/forum/showthread.php?t=6931&

Glad to hear it works.