Refreshed,

Is it normal that the capture module varies ~1 unit the capture of an stable
sqare signal in all the range of frecuencies?
4000Hz 250 and  251
2000Hz 500 and  501
800Hz 1250 and 1251
What this capture means?
There is something wrong in my interrupt routine?

Thank you in advance.

Dennis Crawley
Argentina.


----- Original Message -----
From: "Dennis Crawley" <proyectosenpic@YAHOO.COM.AR>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, April 12, 2004 6:30 PM
Subject: [PIC:] Capture


> Hi,
> The capture module can be configured as one rising edge detector. If TMR1
is
> running free and the capture module is armed, CCPx can take two snapshots
of
> TMR1. The pulse width can be calculated applying 16 bit unsigned math:
>
> PULSE_WDTH = NEW_CAPT - OLD_CAPT
>
> TMR1 is configured in a way that each unit values one microsecond.
> Since I don't have a stable wave generator to test it, I've done a simple
> ON-OFF 50% duty oscillator with a 16F873. Using Andy Warren loop
> generator (625 Inst-cy) achieves full precision in MPLAB simulator, so I
use
> some crystals to change the frequency and I've obtained these captures:
> 20Mhz = 250 and  251 (us)
> 10Mhz = 500 and  501
>  4Mhz =1250 and 1251
>
> Q1: What means that jumping from 0 to 1 and 1 to 0?
> Q2: If it is normal, has a name?
> Q3: CCPx has lost one pulse from TMR1?
>
> Configuration:
> 16mhz crystal
> TMR1 1:4
> CCP2 prescaler 1:1
> CCP2 rising edge
> The whole process is fired once every 100ms, by now.
>
> ;======================================================================
> ; CCP2 ISR : PIE2,CCP2IE bandera en PIR2,CCP2IF
> ;======================================================================
> PIR2_CCP2IF_Handler:
>         BSF    STATUS,RP0
>         BCF    PIE2,CCP2IE
>         BCF    STATUS,RP0
>         BCF    PIR2,CCP2IF
>
> ;Test if it is the first pulse
>         btfsc  PWMErrorFlags,SnapOnGo
>         goto   SndSnap
> ;First pulse
>         BSF    PWMErrorFlags,SnapOnGo
>         movfw   CCPR2H
>         movwf   CCP_H_OLD
>         movfw   CCPR2L
>         movwf   CCP_L_OLD
>
>         BSF    STATUS,RP0
>         BSF    PIE2,CCP2IE
>         BCF    STATUS,RP0
>         GOTO    _Interrupt_handler
>
> SndSnap:
>         BCF     INTCON,PEIE
>         BCF     PWMErrorFlags,SnapOnGo
>
>         movfw   CCPR2H
>         movwf   CCP_H_NEW
>         movfw   CCPR2L
>         movwf   CCP_L_NEW
>
> ;Measure the width
>         movf    CCP_L_OLD, w
>         subwf   CCP_L_NEW, f
>         btfss   STATUS, C
>         decf    CCP_H_NEW, f
>         movf    CCP_H_OLD, w
>         subwf   CCP_H_NEW, f
>         bsf     PWMErrorFlags,SnapNewCap
>
>         GOTO    _Interrupt_handler
>
>
> Thank you in advance.
>
> Dennis Crawley
> Argentina
>
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