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Passing variables from C to Assembler

 
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darahayes



Joined: 05 Mar 2009
Posts: 15

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Passing variables from C to Assembler
PostPosted: Thu Nov 21, 2013 7:43 am     Reply with quote
Could some one please show how the passing of variables is achieved between a Pic c program and an inline #ASM routine and perhaps how we can get ASM modified variables back into the C program once again ,
I am working with a PIC18F device and using the CCS c compiler ver 4.141
my search for this topic on this forum has not given any meaningful results
many thanks
Gabriel



Joined: 03 Aug 2009
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PostPosted: Thu Nov 21, 2013 7:49 am     Reply with quote
A variable is stored in a ram location with a specific address... you can reference this adress directly on ASM.
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dyeatman



Joined: 06 Sep 2003
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PostPosted: Thu Nov 21, 2013 7:54 am     Reply with quote
http://www.ccsinfo.com/forum/viewtopic.php?t=50807&highlight=asm
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Ttelmah



Joined: 11 Mar 2010
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PostPosted: Thu Nov 21, 2013 7:54 am     Reply with quote
You don't have to!....

You can just use the C variables in assembler.
Code:

void main()
{
   int a;
   a=10;
   
#asm
   MOVLW 4
   ADDWF A,W
   MOVWF A
#endasm
   //'a' is now 14...

  while (TRUE) ;
}

It will automatically bank switch to select the variable if needed.
However it is now almost totally unnecessary to use assembler in CCS. Just about everything that can be done in assembler can be done directly from the language without using this.

What do you want to do?.

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