Hi all,
I'm requesting some help.=A0 I need to measure a frequency range of
apporximately 700hz to 4000hz.=A0 The frequency will be in the form of a
squarewave.=A0 It is fed into RC2 (CCP1) on a PIC16F876A connected to a
20Mhz crystal.=A0 I need this to be accurate to 1/25Hz or better.=A0 If
possible I prefer to read 512 cycles to keep the aquisition time to a
minimum.=A0 I tried to write a routine but=A0the accuracy is not quite
there and it doesn't work below about 1200hz.=A0 I am using basic but I
wrote a routine in assembly to imbed in the basic program for this.=A0 I
have issues in this routine but I have been unable to figure out
where.=A0 I have searched for sample routines but haven't been able to
find anything quite close to what I'm trying to accomplish or any
explanations that I can understand.=A0 I'm using 1:1 on timer1 and
capturing every 16th rising edge.=A0 Any help or code is greatly
appreciated.=A0 I need to solve this quickly.
Thanks,
Fran
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
'*** Variables used in math ASM subroutine ********
Dim accu as longint absolute 0x35      'test0,test1,test2
Dim count As Word absolute 0xA4      'count is the same as <TMR1L:TMR1H>
Dim tmr1tmpl As byte absolute 0xA4   'tmr1tmpl used to store first capture
Dim tmr1tmph As byte absolute 0xA5  'tmr1tmph used to store second capture


for j=3D1 to 32

ASM

BCF STATUS,RP0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0;Bank 0
CLRF T1CON=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0 ;clear t1con
MOVLW 0x07=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0  ;w =3D 07h
MOVWF CCP1CON=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ;Enable=
 ccp1 for 16 rising edges
BCF PIR1,2 ;clear flag CCP1
INI:
BTFSS PIR1,2                           ;testing flag
GOTO INI
BSF T1CON,0                           ;timer 1 enabled
BCF PIR1,2 ;clearing flag CCP1
X:
BTFSS PIR1,2                           ;flag =3D 1?
GOTO X
BCF T1CON,0                           ;turn off timer1
BCF PIR1,2                               ;clear flag CCP1
CLRF TMR1L                             ;clear register TMR1L
CLRF TMR1H                            ;clear register TMR1H

END ASM

tmr1tmpl=3DCCPR1L                     ' These 2 lines put the counter value=
 in
tmr1tmph=3DCCPR1H                   ' the variable count
accu=3Daccu+count
next j
                                                ' here accu variable
holds total timer ticks for 512 cycles

-- =

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