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rs232 problems

 
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rs232 problems
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rs232 problems
PostPosted: Wed Sep 29, 2004 12:17 pm     Reply with quote
I wrote a small application to read from a GPS module and send whatever it reads to the PC.

Code:
#include <16f876.h>
#include <string.h>
#fuses XT, NOPROTECT, BROWNOUT, LVP, NOWDT, PUT
#use delay (clock=4000000)

#use rs232(baud=2400,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,stream=GSM)
#use rs232(baud=4800,parity=N,xmit=PIN_C4,rcv=PIN_C5,bits=8,stream=HOSTPC)
#use rs232(baud=4800,parity=N,xmit=PIN_C2,rcv=PIN_C3,bits=8,stream=GPS)


.
.

fprintf(HOSTPC,"Ready");

.
.

    while(1)
    {
      c = fgetc(GPS);
      fputc(c,HOSTPC);

    }

When I run that program "Ready" is displayed correctly on my terminal. When the GPS unit starts to send the NMEA data I start to see garbage on my terminal except for the '$' and ',' characters. Both are displayed correctly and other characters are nothing but garbage.

I connected the GPS unit directly to my PC using max232 and it dumps the NMEA data correctly w/o any problem on my terminal.

One more thing to say, I am using interrupt handler to deal with the GSM stream.

Code:
#INT_RDA
rda()
{
   int8 c;
   c=fgetc(GSM);
   if(c==10)
   {
      sbuf[scnt-1]=0;
      scnt = 0;
      sflag=1;
   } else
   {
      sflag = 0;
      sbuf[scnt++]=c;
   }
}


Any idea?
Humberto



Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata

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PostPosted: Wed Sep 29, 2004 12:46 pm     Reply with quote
In your interrupt handler, I would try the following just to quit the interrupt handler as soon as posible.

Code:

#INT_RDA
rda()
{
int8 c;
     
    if(kbhit(GSM))
      {
       c=fgetc(GSM);
       if(c==10)
         {
          sbuf[scnt-1]=0;
          scnt = 0;
          sflag=1;
         }else
         {
          sflag = 0;
          sbuf[scnt++]=c;
         }
     }
}


best wishes,

Humberto
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