Post by thread:Pulse Measurement Loop

>I recall a while ago somebody (Scott?) posted a routine for very accurate >measurement of pulses. > >I need to measure a 500-2500 instruction cycle pulse at 4 or better cycle >resolution on a standard PORTB pin (not int-on-change) in a '711. > >I also need to catch and report invalid (short or long) pulses. > >Anybody have that posting? I posted the orginal question and several very helpful souls found the answer I am now using. The core of the routine came from Scott Dattalo. Enjoy! The following is snipped from one of my messages to Scott: BTW: the code works VERY well. Its being used to measure the pulse duty cycle ratio from Analog Devices TMP03 / 04 temperature sensors and can resolve down to fractins of a degree (far more accuracy than the sensor). I cleaned the normalize part of the routine up slightly as follows at the end of this message. The entire measurement routine (wait for HI, wait for LO, measure LO, measure HI, test for noisy signal, normalize everything, multiply HI pulse by constant, divide by LO pulse, average 16 samples) takes about 400 code spaces - left me lots of room for the rest of the project in a 12c508. ;up to 19 bit pulse timer with 3 cycle resolution ;concept by Scott Dattalo, this version by Dwayne Reid ;now measure HI period clrf MH_low clrf MH_mid clrf MH_high ;used as known zero for main loop MH_loop btfss PULSE goto MH_1st movlw 1 btfss PULSE goto MH_2nd addwf MH_low,F btfss PULSE goto MH_3rd rlf MH_high,W ;get C into W lsb (add 0 or 1 to next byte) btfss PULSE goto MH_4th addwf MH_mid,F ;add previous carry btfss PULSE goto MH_5th ;use either line below (not both) btfss MH_mid,5 ;5 = 16 bits; 6 = 17 bits; 7 = 18; skpc = 19 ; skpc ;5 = 16 bits; 6 = 17 bits; 7 = 18; skpc = 19 btfss PULSE goto MH_6th nop ;spare cycle! btfss PULSE goto MH_7th clrwdt btfsc PULSE goto MH_loop MH_8th incf MH_high,F ;MH_high now used to accumulate LSBs MH_7th incf MH_high,F MH_6th incf MH_high,F MH_5th ;use either line below (not both) btfsc MH_mid,5 ;5 = 16 bits; 6 = 17 bits; 7 = 18; skpnc =19 ; skpnc ;5 = 16 bits; 6 = 17 bits; 7 = 18; skpnc =19 goto overflow ; subwf MH_mid,F ;undo increment, if any incf MH_high,F MH_4th incf MH_high,F MH_3rd decf MH_low,F ;undo increment incf MH_high,F MH_2nd incf MH_high,F MH_1st ;normalize high period movfw MH_high ;get LSB count into w clrf MH_high ; clrc ;make room for lower 3 LSBs rlf MH_low,F ; (shift everything to the left 3 bits) rlf MH_mid,F rlf MH_high,F ; rlf MH_low,F rlf MH_mid,F rlf MH_high,F rlf MH_low,F rlf MH_mid,F rlf MH_high,F ;none of this affects LSB count in w iorwf MH_low,F ;put LSBs into low byte ;done! Dwayne Reid <spam_OUTdwaynerTakeThisOuTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (403) 489-3199 voice (403) 487-6397 fax