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hayee
Joined: 05 Sep 2007
Posts: 252
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| can edge be change in interrupt routine? |
 Posted: Thu Nov 01, 2012 5:34 am |
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Hi,
I want to know that, can we change the edge in the interrupt routine like
| Code: |
#int_ext
void ext_isr()
{
.....
ext_int_egde(0,H_to_L);
...
}
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temtronic
Joined: 01 Jul 2010
Posts: 9243
Location: Greensville,Ontario
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| Posted: Thu Nov 01, 2012 5:54 am |
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maybe...
As presented we don't have enough information to say 'yes' or 'no'.
To be fair...SOME PICS allow the edge to be changed on some of the pins but we don't know which PIC you're using.
Also I think you've got a 'typo' , ...egde should be ...edge.
You should create a complete program and compile, then run it, and see what happens.
Read the datasheet for your PIC to see which pins allows what kind of interrupts and then read the compiler to see which functions are available.
hth
jay |
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hayee
Joined: 05 Sep 2007
Posts: 252
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| Posted: Thu Nov 01, 2012 6:03 am |
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thanks temtronic
I am using 16f870. I write the code and compiled it, but its not working. I always got an interrupt on the edge which I described in initialization.
What I want to do is to measure the frequency and ON/OFF time of the signal, that's why I want to use interrupt on every edge. Is there any other way to measure ON/OFF time? |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19539
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| Posted: Thu Nov 01, 2012 9:42 am |
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OK.
You certainly can change the edge on the 870. However the reason it probably doesn't work is that you get 'out of sync' at start-up. If the chip interrupts when you set the edge at start-up (common), then if your interrupt code thinks it has triggered on the 'other' edge, and things go wrong from here....
The other question is 'how long is the pulse'. Remember it takes a very significant time to get into the handler, and again if the pulse is short there may not physically be time to get into the handler and out again.
| Code: |
#int_ext
void ext_isr(void) {
if (input(PIN_B0)==1)
//signal is high
ext_int_edge(H_to_L);
else
ext_int_edge(L_TO_H);
...
}
//You only need the leading number on chips that support more than one
//INT input.
//Here you check the current level, to set which edge to detect. Avoids
//problems....
//In main
ext_int_edga(H_TO_L);
clear_interrupts(INT_EXT); //setting the edge can trigger the interrupt
enable_interrupts(INT_EXT);
enable_interrupts(GLOBAL);
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Note clearing the interrupt after setting the edge - setting the edge can
cause the interrupt to set - this then can lead to you getting to the interrupt on the opposite edge from what you expect....
Best Wishes |
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Gabriel
Joined: 03 Aug 2009
Posts: 1067
Location: Panama
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| Posted: Fri Nov 23, 2012 12:06 pm |
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Just use the Port_b interrupt on change pins...
you dont need to change any edge or what not.. just make sure to write or read the port in the ISR.
G.
_________________
CCS PCM 5.078 & CCS PCH 5.093 |
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Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
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| Posted: Sat Nov 24, 2012 11:43 am |
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| Quote: |
Just use the Port_b interrupt on change pins...
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According to "PIC16 and PIC18 Family Reference Manuals"
http://ww1.microchip.com/downloads/en/DeviceDoc/31009a.pdf
"The interrupt on change feature is recommended for wake-up on key depression and operations where PORTB
is only used for the interrupt on change feature. Polling of PORTB is not recommended while using the interrupt
on change feature. Other data sheets specifically warn that interrupts can be lost by polling PORTB, and Microchip
forum users have reported cases of interrupts being lost."
Hence this issue is a problem if you have either:
- A single pin that can change twice in a period approximately equal or less than your RBIF interrupt handler's latency, or
- Two or more pins that can both change within a period approximately equal to your RBIF interrupt handler's latency.
This issue has been corrected in the PIC30 core by using the output of the input latch as the input to the change latch.
It has also been corrected in the enhanced midrange line (PIC16F1xxx).
Humberto |
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ERICOO
Joined: 13 Jun 2011
Posts: 14
Location: NIGERIA
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| Posted: Sun Nov 25, 2012 2:31 am |
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| yes the edge can be changed within the interrupt routine, but just be sure that you disable the specific interrupt within the routine before changing the edge and re enable it before leaving the interrupt routine. |
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