Capture loop exit

[spcw1234]

I am using a capture module to measure RPM with a PIC16F628A. It works very well, but if the motor isn't running there will be no pulse so I am stuck in an endless loop waiting for the pulse. I need to do other things on the pic, so this isn't good. Besides incrementing a value, how else can I add a failsafe to exit the loop?

Trash:
  If Capture = 0 then
    Goto Trash          'stuck in loop if no capture
  endif

  T1CON.0=1              'starts timer
  Capture=0               'trash first capture

CaptureLoop:
  If Capture = 0 then
    Goto CaptureLoop
  endif
T1Con.0=0  
period.LowByte=CCPR1L
period.HighByte=CCPR1H

In the CaptureLoop I can look for a timer1 overflow flag which would work, but the trash loop the timer isn't running, so that wouldn't work.

[HenrikOlsson]

Hi Shawn,
As far as I can see you have two options, software and hardware.
Use a timer interrupt (or poll the interrupt flag) to abort the wait loop OR use a software "timer" to abort the wait loop. If you, for whatever reason, don't want to increment a variable (software "timer") inside your waitloop then the only option left is hardware. I see no reason why you can't use TMR1 if you want to, just reset it when the trigger comes.

I've never used the capture module though so I may be missing something.

/Henrik.

[spcw1234]

Thanks Henrik,
I was concerned that stopping the timer and restarting it would throw off the measurement, as I am sure it would. I tried it with just clearing the timer registers and tested it, and all seems good. Just checking for a timer overflow which if occurred will exit the capture routine.

  TMR1H=0      'Clear 8-bit register                              
  TMR1L=0      'Clear 8-bit register
  T1CON.0=1    'starts timer  
  overflow=0   'Clear overflow bit
  capture=0    'Clear Timer
Trash:
  If Capture = 0 then
     if overflow=1 then 
       rpm=0
       T1Con.0=0  
       return
       endif    
    Goto Trash          
  endif
  TMR1H=0      'Clear 8-bit register                              
  TMR1L=0      'Clear 8-bit register
  Capture=0    'waste first capture
  Overflow=0   'Clear overflow bit     
CaptureLoop:
  If Capture = 0 then
     if overflow=1 then 
       rpm=0
       T1Con.0=0  
       return  
       endif  
    Goto CaptureLoop
  endif
T1Con.0=0  
period.LowByte=CCPR1L
period.HighByte=CCPR1H
  TMR1H = 0
  TMR1L = 0
  Capture = 0
  Overflow = 0