Time diference in microseconds

[leonel]

I´m trying to measure the time diference between two signals and I don´t know how to do. The time diference is in order of microsecods or miliseconds, and I have to have an accurate precision.
Can anybody help in the code that I have to write?
Thank you.

[mister_e]

the easiest way, and the most accurate one, will be to use internal timer. Start the timer with a rising or falling edge of your first signal, stop it at the next falling or rising edge, place the result of the counter into a variable, thennn switch to your next signal and do the same test. at the end compare both results

At :
4MHZ you'll have a accuracy of 1uSec
8MHZ you'll have a accuracy of .5uSec
and such

Which PIC are you using ??? at which speed?

[leonel]

I'm thinking to use 16F874 at 4MHz.
It´s possible to post some code, if for example we have one signal in RA1 and another in RA2 because I´m not too familiar with assembler... I´m working with PICBasicPro.
Thank you.

[leonel]

Look if this code it works to measure two signals...

if portb.1=1 then
T1CON=1 " start timer
while portb.2 = 0
if portb.2=1 then
T1CON=0 " stop timer
var = TMR1 " my variable comes with the value of the time diference in microseconds
endif
wend
endif

[mister_e]

try this one

' Program to measure time on two pins in a 1uSec increment
' Using PIC16F874 with TIMER1

TRISA=255  ' Set PORTA as INPUT
ADCON1 = 7 ' disable analog to digital converter

T1CON = 0  ' set timer clock source to internal (fosc/4)

Signal1TIME var word   
Signal2TIME var word
Signal1     var PORTA.1
Signal2     var PORTA.2

Start:

' measure period on RA.1
'
TMR1L=0
TMR1H=0
while signal1=0 ' waiting for rising edge
wend
T1CON.0 = 1 ' start Timer1
While signal1 ' wait for falling edge
wend
while signal1 = 0 ' wait for the next rising edge
wend
T1CON = 0 ' stopTimer
signal1time.lowbyte = TMR1L
Signal1time.highbyte = TMR1H


' measure period on RA.2
'
TMR1L=0
TMR1H=0
while signal2=0 ' waiting for rising edge
wend
T1CON.0 = 1 ' start Timer1
While signal2 ' wait for falling edge
wend
while signal2 = 0 ' wait for the next rising edge
wend
T1CON = 0 ' stopTimer
signal2time.lowbyte = TMR1L
Signal2time.highbyte = TMR1H

lcdout $fe,1  ,"RA1 : ",#signal1," uSec",_
       $fe,$c0,"RA2 : ",#signal2," uSec"

pause 2000
goto start

This is suppose to work.

[mister_e]

oups change the variable in the LCDOUT...

must be

lcdout $fe,1  ,"RA1 : ",#signal1TIME," uSec",_
       $fe,$c0,"RA2 : ",#signal2TIME," uSec"

[Kman]

Mister e,
How would you do it if you wanted to use 1 pin as an input?

[mister_e]

you mean??? check two different signal on one pin?

[leonel]

Hi. Thanks for your code...
What about using this code (your code with a little changes ) to measure the time that the signal stays high, because I think that with your code I have the problem that I could find the signal in an high level and didn´t count the correct time!
Take a look...

code:


' Program to measure time on two pins in a 1uSec increment
' Using PIC16F874 with TIMER1

TRISA=255 ' Set PORTA as INPUT
ADCON1 = 7 ' disable analog to digital converter

T1CON = 0 ' set timer clock source to internal (fosc/4)

Signal1TIME var word
Signal2TIME var word
Signal1 var PORTA.1
Signal2 var PORTA.2

Start:


‘ I will measure the time staying high, but only in the second period
‘ because I have a little chances that when I go to next pin “find” 'the pin in middle of a high level and I didn´t count the correct time

' measure time that RA.1 stays high
TMR1L=0
TMR1H=0
while signal1=0 ' waiting for rising edge
wend
While signal1 ' wait for falling edge
wend
while signal1 = 0 ' wait for the next rising edge
wend
T1CON.0 = 1 ' start Timer1
While signal1 ' wait for falling edge
Wend
T1CON = 0 ' stopTimer

signal1time.lowbyte = TMR1L
Signal1time.highbyte = TMR1H


' measure time that RA.2 stays high

TMR1L=0
TMR1H=0
while signal2=0 ' waiting for rising edge
wend
While signal2 ' wait for falling edge
wend
while signal2 = 0 ' wait for the next rising edge
wend
T1CON.0 = 1 ' start Timer1
While signal2 ' wait for falling edge
Wend
T1CON = 0 ' stopTimer
while signal2 = 0 ' wait for the next rising edge
wend

signal2time.lowbyte = TMR1L
Signal2time.highbyte = TMR1H

lcdout $fe,1 ,"RA1 : ",#signal1TIME," uSec",_
$fe,$c0,"RA2 : ",#signal2TIME," uSec"
pause 2000
goto start

[mister_e]

try with this

' measure time that RA.1 stays high
TMR1L=0
TMR1H=0

     ' test if the signal is already high
     '
Signal1HIGH:
if signal1 then Signal1HIGH

     ' wait for the rising edge
     '
while signal1 = 0
wend

     ' signal is now high... let's count the "hi" time 
     '
T1CON.0 = 1 ' start Timer1

While signal1 ' wait for falling edge
wend

T1CON = 0 ' stopTimer

     ' store the result
     '
signal1time.lowbyte = TMR1L
Signal1time.highbyte = TMR1H

[leonel]

Thank´s a lot...
I suppose your code works but I don´t think these week I´ll have time to test it, because I´m working with the hardware...
But when I have news I´ll tell you.
Regards
Leonel Monteiro

[leonel]

Can anybody explain me what´s wrong in these code...
I want to turn led on and off in each 5 seconds, but it didn´t wait 5 seconds. It is much less, about 50ms
Sorry but variables and comments are in portuguese

'este ficheiro é apenas para testar algumas funcionalidades da placa

DEFINE OSC 4 'o programa irá correr a 4MHz

ADCON1 = $06 'indica que todas as entradas são digitais
TRISA = $3F 'estou a colocar RA.0, RA.1, RA.2, RA.3, RA.4 e RA.5 como entradas e o resto como saídas
TRISB = $FF 'estou a colocar tudo como entradas
TRISC = $00 'estou a colocar tudo como saídas
variavel var word
start:
portc.3 = 1
gosub tempo_ligado
portc.3 = 0
portc.2 = 1
gosub tempo_ligado
portc.2 = 0
portc.1 = 1
gosub tempo_ligado
portc.1 = 0
goto start

tempo_ligado:
T1CON.0 = 1 'inicio o timer
while variavel < 80
if pir1.0 = 1 then
variavel = variavel + 1 'a variavel incrementa a cada 0.06seg.
'colocando a 80 esperamos 5seg
endif
wend
pir1.0 = 0
T1CON.0 = 0 'paro o timer
variavel = 0
TMR1L = 0
TMR1H = 0
return

[Ingvar]

Try ....

tempo_ligado:
T1CON.0 = 0 'paro o timer
pir1.0 = 0
variavel = 0
TMR1L = 0
TMR1H = 0
T1CON.0 = 1 'inicio o timer
while variavel < 77
if pir1.0 = 1 then
variavel = variavel + 1 'a variavel incrementa a cada 0.06seg.
'colocando a 80 esperamos 5seg
pir1.0 = 0
endif
wend
T1CON.0 = 0 'paro o timer
return

[leonel]

Thank´s...
Your code works.