GPS clock timing !

[bethr]

Dear Forum:

I'd like to build a small Clock with GPS time-sync, look, I'm using the Darrel instant interrups to drive the Timer 1 clock, it works great ! (Thanks Darrel !), but when I tried to read the GPS data (over Pin RB1) there is a lot of missed/corrupted bytes in my buffer, something like this:

the first lcd line is the RMC message data (corrupted in this case) and the second line display the RTC registers, (plese note tha my LCD was broken so the lower line is wrong )

this is the code

'''''''''''''' INCLUDES ''''''''''''''''''''''''''''''''''''	
	DEFINE OSC 4 
	INCLUDE "DT_INTS-18.bas"
	INCLUDE "ReEnterPBP-18.bas"
	INCLUDE "Elapsed_INT-18.bas"  
	INCLUDE "LCDPICDEM2.BAS"		' it runs on PIDEM2 PLUS Board

''''''''''''' VARIABLES ''''''''''''''''''''''''''''''''''''	
		j    var byte
		rmc  var byte[100]	' this gets RMC data
		led1 var  portb.2
		b0   var byte
		adcon1 =$07
		trisa.2 = 0
		trisa.4 = 1
		trisb.1 = 1
		trisb.2 = 0
		trisb.0 = 1
		trisc.2 = 0
	    porta.2 = 0
		gps var portb.1
	 	spk    var portc.2

''''''''''''' CODE ''''''''''''''''''''''''''''''''''''	
	
init:	
	ASM
	INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
	        INT_Handler   TMR1_INT,  _ClockCount,   PBP,  yes
	        endm
	INT_CREATE                 
	ENDASM
	T0CON = %10011010
	@    INT_ENABLE  TMR1_INT      
	GOSUB ResetTime
	GOSUB StartTimer           
	hours = 11 : minutes = 30: seconds = 0
    
Start:
	LCDOUT $FE,1                    ' Initialize LCD
	PAUSE  200	
	lcdout $fe,2,"Starting ..." : pause 500

Main:
 
	serin2 gps,188,1000,no_gps,[wait("MC"),str rmc\15\10]	'15 bytes only for testing () wait for RMC message
 
	lcdout $fe,$c0,"Time : ",dec2 hours,":",dec2 minutes,":",dec2 seconds
 
	lcdout $fe,2,"$",str rmc\15 :pause 500						' these are the bytes as captured !
	goto main

no_gps:
	lcdout $fe,2,"Np Gps stream ": pause 500
	goto  main
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

my first idea to fix it,was stop the timer just before get the gps data stream, like this:

	gosub stoptimer
	serin2 gps,188,1000,no_gps,[wait("MC"),str rmc\15\10]	'15 bytes only for testing () wait for RMC message
	gosub starttimer

using above lines my LCD looks like this:

looks good !!!


but here, I have a problem with the time !, this make delay on the RTC, If I just was updated my clock register each ten minutes or so, that work out very well, but I want to keep my RTC all the time, (for logging timed-stamp GPS locations by example).

I knew this is a time issue (software generated timing "serin2"), another plan is to use the internal UART build in my pic (i'm using a18f452), but my GPS only outputs TTL levels this create interfacing problems, how can I get working this project?

Thanks !!!