16F877@4Mhz calculate Pulsin to RPM

[Darrel Taylor]

Hi Leigh,

Just took a quick look at your program, and I can't answer all those questions, but did notice one thing.

The capture function of the CCP simply latches the Timer value into the CCPRH:L register when the specified event occurs. In this case thats after 4 RISING edges. To get a meaningfull result, the timer has to be started at the same time as the CCP starts counting it's 4 periods.

You can just leave the timer turned off and let it capture 0 the first time, then as soon as the CCP1IF (PIR1.2) is raised, imediately start the timer, then reset the CCP1IF. On the next capture you should have a valid result.

I don't know about all the rest, but one thing at a time usually works best.

Maybe something like this

CCP1CON = %00000110			' Enable the CCP1 capture, every 4th rising edge
loop:
T1CON = %00010000 			' TMR1 prescale=1:2  Timer OFF
TMR1H = 0                               ' Zero the Timer
TMR1L = 0
capture = 0
StartLoop:
	IF (capture = 0) Then StartLoop	' Wait here for the first capture
                T1CON.0 = 1             ' Start the Timer
                capture = 0             ' Reset  the capture flag
CaptureLoop:
	IF (capture = 0) Then CaptureLoop	' Wait here until captured
	period.lowbyte = CCPR1L		' Store the captured value in
	period.highbyte = CCPR1H	' period variable

DT