PulsIn question.

[Peter Oors]

Can somebody give me an answer?
How many µs does the PulsIn command take?
I would like to measure a pulsetrain with 2 kind of pulses,
91µs high and 13µs low (long), 13µs high and 91µs low (short).
I use the 16F819 and the 16F628 with 20MHz X-tal.

[air1kdf]

I would also like to know how long the pulsin command overhead itself takes with a given frequency.

For example assume that the pulsin returned 1000 with a 20Mhz crystal would be 2000 microseconds. If It started measuring just after a change in state it would have taken say 1999 + 2000 or 3999 microseconds. Now add the overhead of the command itself and that would be the total time that the command takes.

[Peter Oors]

Today I measured a time from the end of a pulse to the end of the PulsIn command of about 12us.
For me the PulsIn command is useless.
In assembler it's the best way, but I don't know how to do this in assembler.

[mister_e]

Even in PBP you'll be able to do it with a decent result. Just use the internal timer. The following example is more than enough to start.

    '    Pulse High and Low Timer
    '    ========================
    '
    '    File name  : PulseHighLowTimer.bas
    '    Company    : Mister E 
    '    Programmer : Steve Monfette
    '    Date       : 13/01/2006
    '    Device     : PIC16F88
    '
    
    '
    '        This program measure and send to PC, the value of incomming pulses. 
    '    The program will send measure of High pulse and Low Pulse length in uSec.
    
    '
    '    Hardware configuration
    '    ======================
         DEFINE OSC 20
         DEFINE LOADER_USED 1
         TRISB = %00000100      ' RB2 as input => Serial RX
         TRISA = 255            ' PORTA As input
         CMCON = 7              ' Disable analog comparator
         ANSEL = 0              ' Disable all A/d
         T1CON = 0              ' TIMER1:
                                '        Clock Internal
                                '        Pre-scaller 1:1
    '                      
    '    Hardware connection
    '    ===================
         SignalInput       var PORTA.2
         
    '
    '    Serial Communication definition
    '    ===============================
         DEFINE HSER_RCSTA 90h
         DEFINE HSER_TXSTA 24h
         DEFINE HSER_SPBRG 129 ' 9600 Bauds
         DEFINE HSER_CLROERR 1
    '
    '    Alias Definition definition
    '    ===========================
         T1ON              var T1CON.0

    '   
    '    Variables definition 
    '    ===================
         PulseHigh          var word
         PulseLow           var word

    '
    '    Software/Hardware initialisation
    '    ================================
         CLEAR
         GOSUB ClearTimer
    '
    '    ////////////////////////////////|\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\        
    '
    '                             Program Start Here                               
    '
    '    ////////////////////////////////|\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\        
    '    
Start:
    '
    '    Waiting for falling edge
    '    ========================
         '  
         WHILE SIGNALINPUT=0 : WEND
         WHILE SIGNALINPUT=1 : WEND
    '
    '    Measure low pulse
    '    =================
         '    
         T1ON=1                     ' start Timer
         WHILE SIGNALINPUT=0 : WEND ' wait for next rising edge
         T1ON=0                     ' stop timer
         PULSElow.HIGHBYTE=TMR1H    ' store results 
         PULSElow.LOWBYTE=TMR1L     ' 
         pulselow=pulselow / 5      ' 1 tick = 0.2 Usec @ 20MHZ
                                    ' Divide by 5 to have 1 uSec
                                    ' Resolution
         gosub Cleartimer           ' reset Timer1 register (TMR1L, TMR1H)
    '
    '    Waiting for rising edge
    '    =======================
         '
         while Signalinput=1 : Wend
         while signalinput=0 : wend
    '
    '    Measure high pulse
    '    ==================
         '    
         T1ON=1                     ' Start timer
         WHILE SIGNALINPUT=1 : WEND ' wait for next falling edge
         T1ON=0                     ' Stop Timer
         PULSEhigh.HIGHBYTE=TMR1H   ' Store result
         PULSEhigh.LOWBYTE=TMR1L    '
         pulsehigh=pulsehigh / 5    ' match results to 1 uSec resolution
         gosub Cleartimer           ' reset Timer1 register (TMR1L, TMR1H)
         
    '
    '    Send results to PC via RS-232
    '    =============================
         '     
         hserout ["PulseLow =",dec pulselow, " uSec",13,10,_
                  "PulseHigh=",dec pulsehigh," uSec",13,10,_
                  rep "*"\50,13,10]
         pause 1000
         goto start              

ClearTimer:
    TMR1L=0
    TMR1H=0
    RETURN

I agree, you can have a bit more accuracy in pure assembler... but test with the above first.

It's only one way to do it... that's the results of a 10 minutes coding... on friday 13

[Peter Oors]

Thanks very much mister_e, you are a great help.
The text was very helpfull. The accuracy is perfect for me.

When I measured more pulses, there was a problem.
Something goes wrong.
Dividing by 5 gives problems.

=====================================
T1ON=1 ' start Timer
While SIGNALINPUT=0 : Wend ' wait for next rising edge
T1ON=0 ' stop timer
PULSElow.HIGHBYTE=TMR1H ' store results
PULSElow.LOWBYTE=TMR1L '
pulselow=pulselow / 5
=====================================

The above part I changed in (not the most beautiful way):

Start:
GoSub meten
PULSEhigh1.HIGHBYTE=TMR1H ' Store result
PULSEhigh1.LOWBYTE=TMR1L
GoSub meten
PULSEhigh2.HIGHBYTE=TMR1H ' Store result
PULSEhigh2.LOWBYTE=TMR1L
GoSub meten
PULSEhigh3.HIGHBYTE=TMR1H ' Store result
PULSEhigh3.LOWBYTE=TMR1L
GoSub meten
PULSEhigh4.HIGHBYTE=TMR1H ' Store result
PULSEhigh4.LOWBYTE=TMR1L
GoSub Cleartimer
GoSub meten
PULSEhigh5.HIGHBYTE=TMR1H ' Store result
PULSEhigh5.LOWBYTE=TMR1L
GoSub meten
PULSEhigh6.HIGHBYTE=TMR1H ' Store result
PULSEhigh6.LOWBYTE=TMR1L
GoSub meten
PULSEhigh7.HIGHBYTE=TMR1H ' Store result
PULSEhigh7.LOWBYTE=TMR1L
GoSub meten
PULSEhigh8.HIGHBYTE=TMR1H ' Store result
PULSEhigh8.LOWBYTE=TMR1L
GoSub meten
PULSEhigh9.HIGHBYTE=TMR1H ' Store result
PULSEhigh9.LOWBYTE=TMR1L
GoSub meten
PULSEhigh10.HIGHBYTE=TMR1H ' Store result
PULSEhigh10.LOWBYTE=TMR1L
GoSub Cleartimer

Pulsehigh1=pulsehigh1 / 5
Pulsehigh2=pulsehigh2 / 5
Pulsehigh3=pulsehigh3 / 5
Pulsehigh4=pulsehigh4 / 5
Pulsehigh5=pulsehigh5 / 5
Pulsehigh6=pulsehigh6 / 5
Pulsehigh7=pulsehigh7 / 5
Pulsehigh8=pulsehigh8 / 5
Pulsehigh9=pulsehigh9 / 5
Pulsehigh10=pulsehigh10 / 5

Write 1, pulsehigh1
Write 2 ,Pulsehigh2
Write 3 ,Pulsehigh3
Write 4 ,Pulsehigh4
Write 5 ,Pulsehigh5
Write 6 ,Pulsehigh6
Write 7 ,Pulsehigh7
Write 8 ,Pulsehigh8
Write 9 ,Pulsehigh9
Write 10 ,Pulsehigh10
Stop
==================================
meten:
GoSub Cleartimer
While signalinput=0 : Wend ' Waiting for rising edge
T1ON=1 ' Start timer, measure High pulse
While SIGNALINPUT=1 : Wend ' Wait for next falling edge
T1ON=0 ' Stop Timer
Return
Cleartimer:
TMR1L=0
TMR1H=0
Return

It works fine, not beautiful, I know.
Thanks for the help.