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RS232 will not start (reliably)

 
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eyewonder300



Joined: 09 Jun 2004
Posts: 52

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RS232 will not start (reliably)
PostPosted: Tue Sep 27, 2005 6:30 pm     Reply with quote
I am using an 18F4680 to receive GPS serial data but can not make it start up every time. The PIC board supplies ground, +12, along with TX/RX on the same cable to the GPS. If I restart the PIC with GPS on, I get no joy. I have put bit-toggle flags in the ISR to check if its even getting there, and it is not.

However, if the GPS is off when I reset the PIC, wait a few seconds, then turn on the GPS, all works as intended. Is there something I need to initialize, or otherwise set up?

As always, help is appreciated

Steve

Code:

//   fuel_gps_test_1.c   Changing to 'F4680

//   Fuel_GPS_test.c
//   This works, BUT:  if GPS quits/powers down, the system will think
//   that the last entry is still current.  Need a way to check whether
//   or not the GPS is working, and if not, set some flag, or other.

#include <18f4680.H>
//#include <16f877a.H>
#device *=16
#FUSES HS,NOPROTECT,NOWDT,NOBROWNOUT,NOLVP,NOCPD,NOWRT
#use delay(clock=10000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) 
#use fast_io(e)

////////////////////////////////////////////////////////////////////////////


#include "noritake_fms_4.h"
#include "ram_address20.h"
#include <stdlib.h>
#include <math.h>

//char gps_text;
//int gps_string_pos;

//char ns_string[5];         //   4 ascii characters + null term to make it a string
//char ew_string[5];

#int_RDA
void RDA_isr(void)
   {
 output_toggle(pin_e0);      //   flag to check entrance to this ISR

    gps_text = getc();          //   char sent from Garmin
    if (gps_text == 0x40)        // 0x40 = @, which is start of gps sentence
      gps_string_pos = 1;      //   start tracking character position   
   else
      gps_string_pos++;
   if(gps_string_pos > 41 && gps_string_pos < 46)
      switch (gps_string_pos)
         {
         case 42: ew_string[0] = gps_text;
                break;
         case 43: ew_string[1] = gps_text;
                break;
         case 44: ew_string[2] = gps_text;
                break;
         case 45: ew_string[3] = gps_text;
                break;
         }

   if(gps_string_pos > 46 && gps_string_pos < 51)
      switch (gps_string_pos)
         {
         case 47: ns_string[0] = gps_text;
                break;
         case 48: ns_string[1] = gps_text;
                break;
         case 49: ns_string[2] = gps_text;
                break;
         case 50: ns_string[3] = gps_text;
                misc_flag.gps_data_in = 1;
                output_toggle(pin_e1);
                break;
         }
   }




void main()
   {
   delay_ms(500);

   vfd_init();
   vfd_putc("\f  GPS receive test");

   set_tris_e(0);
   set_tris_c(0b10100111);
   delay_ms(2000);
   gps_string_pos = 0;
   misc_flag.gps_data_in = 0;

   ns_string[4] = 0x00;         //   write the 'null' character
   ew_string[4] = 0x00;         //   write the 'null' character

   enable_interrupts(global);
   enable_interrupts(int_rda);

   while(TRUE)
      {
    output_toggle(pin_e2);
      if(misc_flag.gps_data_in == 1)      //   both data words are in
         {
         misc_flag.gps_data_in = 0;      //   clear flag
         vfd_gotoxy(1,2);
         vfd_putc("                        ");
         vfd_gotoxy(1,2);
         temp16_1 = atol(ns_string);
         printf(vfd_putc,"%lu",temp16_1);
         vfd_gotoxy(12,2);
         temp16_2 = atol(ew_string);
         printf(vfd_putc,"%lu",temp16_2);
         temp16_1 *= temp16_1;
         temp16_2 *= temp16_2;
         temp16_1 += temp16_2;
         float_1 = temp16_1;
         float_1 /= 10;
         float_2 = sqrt(float_1);
         temp16_1 = float_2;
         }
      }
   }
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue Sep 27, 2005 6:39 pm     Reply with quote
Before we do any other analysis, add the ERRORS parameter
to your #use rs232 statement, as shown in bold below

#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
cmdrdan



Joined: 08 Apr 2005
Posts: 25
Location: Washington

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PostPosted: Tue Sep 27, 2005 6:45 pm     Reply with quote
In addition to PCM's advice on ERRORS, verify the GPS baud rate. Mine runs at 4800 baud, not 9600....

Dan
eyewonder300



Joined: 09 Jun 2004
Posts: 52

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PostPosted: Tue Sep 27, 2005 6:52 pm     Reply with quote
OK, I put the 'ERRORS' parameter in the 'use rs232' line, and it seems to work.

I looked at my CCS manual, and it just said that 'ERRORS' will save the receive errors in a variable, and then reset the error condition. This seems to work for my simple, receive-only application, unless there is something else that I should look at.

Thanks, PCM

Also, I have previously tested live reception (after the forced start-up) of the data of interest, and it appears OK

Steve
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