GPS clock timing !

[Darrel Taylor]

It's alive !!

WooHoo!

I'm wondered why this bit must be set in hi speed if my bps is low ! (4800 bps)

With a 4mhz OSC, I wouldn't consider 4800 "low".

In the datasheet there's a couple tables that show the baud rates vs. OSC freq with BRGH either 1 or 0. With BRGH=0 @ 4mhz, the highest baudrate in the table is 2400. With BRGH=1 it's 19200.

It may still work with BRGH=0, but it's close to the edge, so why not just make it BRGH=1.

I think the HSER_CLROERR 1 may have had the biggest effect.
The GPS will just spit out the data at regular intervals. It doesn't wait for the PIC to be ready. And at 4800 baud it can send a byte every 2ms. So when the program sits in a 500 ms pause, it may receive a couple hundred bytes before the program gets around to looking at the data. There's only a 2 byte buffer in the USART so it causes an Overflow that must be cleared before it will start receiving data again.

BTW currently I'm not using UART interrupts, but . . .
. . . what if . . .

I enable it ?, this give more reliable data incoming form the GPS line ? or it can be dangerous for the RTC health ?

HSERIN is not compatible with USART interrupts.
You would need to parse the incomming data 1 byte at a time with your own handlers.

It's much easier to use HSERIN.

hth,

[bethr]

Yes you're Right, I think that on this way the gps clock work well, there is no problem with it, I have it running & all looks nice !

The program doesn't anything important (just led blinking), and when BTN rb0 is pushed, it gets info from GPS module and update my RTC registers just as i wanted !

 
'BETHR
'''''''''''''' 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
	DEFINE HSER_TXSTA 24h 			' BRGH=1
	DEFINE HSER_RCSTA 90h
        DEFINE HSER_CLROERR 1 			' Hser clear overflow automatically
	DEFINE HSER_SPBRG 51

''''''''''''' VARS ''''''''''''''''''''''''''''''''''''	
		led   var Portb.2
		timeh var byte
		timem var byte
		times var byte
		day	  var byte
		mon   var byte
		yr    var byte
		stat  var byte
		gps   var Portb.1 
		TRISB.2 = 0
		TRISB.0 = 1 
    	         Adcon1 = $07

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''  
	
init:	
	ASM
	INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
	        INT_Handler   TMR1_INT,  _ClockCount,   PBP,  yes
	        endm
	INT_CREATE                 
	ENDASM 

	@    INT_ENABLE  TMR1_INT      
	Gosub ResetTime
	Gosub StartTimer           
	hours = 12 'after reset we always star @12:00:00
    
Start:
	lcdout $fe,1,"GPS Clock "
    Pause 500

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 
Main: 
	While 1
'do something [  something more useful than this :-)  ]
		While (portb.0=1)
			Toggle led
			Lcdout $fe,2,"Date : ",dec2 day,47,dec2 mon,47,dec2 yr
			Lcdout $fe,$c0,"Time : ",dec2 hours,":",dec2 minutes,":",dec2 seconds
		 	Pause 200
		Wend
' if i press rb0 btn update my RTC
		Gosub Update_rtc

	Wend
 
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 
 
''' SUBS ''''
Update_rtc:
'look 4 stream
	lcdout $fe,1,"Updating..."
	Hserin 500,no_gps,[WAIT("MC,"),dec2 TIMEH,dec2 TIMEM,dec2 TIMES,SKIP 5,_
	STAT,skip 30,dec2 day,dec2 mon,dec2 yr]	
'check 4 Valid GPS if so, then update my RTC
	if stat = "A" then
		hours=timeh - 5 : minutes = timem: seconds = times
'no gps so don't update 
	else
		lcdout $fe,1,"Bad Fix" : pause 500
  	endif
	return
'np gps or bad sintax
no_gps:   
	lcdout $fe,1,"No Gps stream" : pause 500
	return
''' END SUBS '''' 

I've had to replace my broken LCD also !!



BIG TNX !

[earltyso]

Hi there Bethr,
I am looking at purchasing a garmin LVS gps for a robot project and I was just wondering what kind of gps you are using? Cost? etc....

[skimask]

Hi there Bethr,
I am looking at purchasing a garmin LVS gps for a robot project and I was just wondering what kind of gps you are using? Cost? etc....

If it has an NMEA serial output line, then you can get usable data out of it.
www.sparkfun.com has a few GPS modules already mounted, ready to use.

[bethr]

Hi there Bethr,
I am looking at purchasing a garmin LVS gps for a robot project and I was just wondering what kind of gps you are using? Cost? etc....

currently I have two modules

this:



http://www.trimble.com/embeddedsyste...?dtID=overview

and this one , a low profile asian embedded device:



both were removed from used equipment, but I know that the trimble module have a cost near to 50 usd (versus qty)
and the other one near to 30 usd

both devices has NMEA ascii output @t vdd levels, trimble vdd=3v3 and asian device vdd=5v

Cheers !!