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External Interrupt in a pin different from RB0

 
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aeroboy



Joined: 26 Apr 2009
Posts: 9

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External Interrupt in a pin different from RB0
PostPosted: Sun Apr 26, 2009 10:35 pm     Reply with quote

Hello,

I am using a 16f877A, when you use an external interrupt you write:

#int_ext
External_Interrupt(){}

Now, that is for PORTB pin RB0, it is possible to define an external interrupt for any pin in PORTB - pins RB1 to RB7?

Thanks.
--Luis
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Apr 27, 2009 12:18 am     Reply with quote

Pins B4-B7 can be used. See this CCS example:
Quote:
c:\program files\picc\examples\ex_pbutt.c


There are other ways to get another individual external interrupt pin.
One of the most well-known ways is to configure Timer1 for an external
clock. Then load Timer1 with 0xFFFF. When it get the first clock edge, it
will roll over to 0x0000 and generate a Timer1 interrupt. You can detect
an edge this way.

You also have the Comparator interrupt.

There might be other possibilities.
aeroboy



Joined: 26 Apr 2009
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PostPosted: Mon Apr 27, 2009 12:08 pm     Reply with quote

Thanks,

Now I have another question, you can define a variable to use like:

unsigned char VALUE;

Can I access the individual bits in this variable?, something like

PIN_VALUE1

Obviously this is not a PIN but maybe there is a way to access the bits.

--Luis
PCM programmer



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Posts: 21708

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PostPosted: Mon Apr 27, 2009 12:24 pm     Reply with quote

If you want a structure of bit variables (int1), see Mark's example:
http://www.ccsinfo.com/forum/viewtopic.php?t=20186
His example allows you to access individual bits in hardware registers.
That's why he uses the #locate directive after each structure.
If you just want to create a structure of bits in a normal variable, then
you don't need the #locate directive.
aeroboy



Joined: 26 Apr 2009
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PostPosted: Mon Apr 27, 2009 1:10 pm     Reply with quote

Thanks,

You mean I have to do this:
Code:
struct {
    unsigned char V0:1;
    unsigned char V1:1;
    unsigned char V2:1;
    unsigned char V3:1;
    unsigned char V4:1;
    unsigned char V5:1;
    unsigned char V6:1;
    unsigned char V7:1;
} VALUE;

But then to access them I just do something like:
Code:
VALUE.Vx=0; or 1

--Luis


Last edited by aeroboy on Mon Apr 27, 2009 1:45 pm; edited 1 time in total
PCM programmer



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PostPosted: Mon Apr 27, 2009 1:24 pm     Reply with quote

Yes, that's correct.

You can also clear the entire structure (all bits) like this:
Code:
value = 0;
aeroboy



Joined: 26 Apr 2009
Posts: 9

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PostPosted: Mon Apr 27, 2009 1:44 pm     Reply with quote

Thanks a lot, that's very useful.

--Luis
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