Help to setup GPS connection.

[mbox]

Hi everyone, I have a GPS with 57600 baud rate and runs on 3.3v, I'm using Pic16F877A with 4Mz crystal. I'm planning to use Serin to read GPS data on PortB.0 and use PortC.6 for Serout to transmit it an LCD or to PC. Do I need to have voltage divider...please give advice.


thanks
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[mackrackit]

Read this
http://www.picbasic.co.uk/forum/showthread.php?t=5667

To give you a good answer we would need the data sheet of the GPS.

[mbox]

Hi,

Read this
http://www.picbasic.co.uk/forum/showthread.php?t=5667

To give you a good answer we would need the data sheet of the GPS.

So far based on what I read I think, voltage divider is not needed because I just want data reading from GPS(LS20031) to MCU or PC.
For GPS to Pic16F877A
GPS Tx--> Mcu Rx
For GPS to PC
GPS Tx--> PC Rx

thanks and regards,
mbox

[ScaleRobotics]

So far based on what I read I think, voltage divider is not needed because I just want data reading from GPS(LS20031) to MCU or PC.
For GPS to Pic16F877A
GPS Tx--> Mcu Rx
For GPS to PC
GPS Tx--> PC Rx

The LS20031 is TTL, and not RS-232. So you will not be able to send it out directly to the PC. You will need something like a max232, or an equivalent to invert the signal levels.

Your PIC should be able to receive the TTL at 3.3v, even though I am guessing the PIC is at 5v. Just don't TX from the PIC to the GPS without a level shifter.

[mbox]

Sorry its been a while, been busy working with other things.

The LS20031 is TTL, and not RS-232. So you will not be able to send it out directly to the PC. You will need something like a max232, or an equivalent to invert the signal levels.

Your PIC should be able to receive the TTL at 3.3v, even though I am guessing the PIC is at 5v. Just don't TX from the PIC to the GPS without a level shifter.

Thanks for the info...one more question, I don't have 20Mz crystal, but I do have 20.945 Cyrstal, can I use it?

thanks in advance,
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[ScaleRobotics]

I have a GPS with 57600 baud rate and runs on 3.3v, I'm using Pic16F877A with 4Mz crystal.

That's a little too high a baud rate for 4 mhz to handle. I think you will have better luck trying 57600 with a 20 mhz crystal.

[mbox]

That's a little too high a baud rate for 4 mhz to handle. I think you will have better luck trying 57600 with a 20 mhz crystal.

okay I will try to change the crystal and update you the results.

thanks and regards,
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[ScaleRobotics]

For the baud rate to be timed right, PicBasic needs to told exactly what frequency the crystal is. PicBasic only allows certain crystals to be defined. Here are the settings allowed: MHz: 3(3.58) 4 8 10 12 16 20 24 25 32 33 40 48 64. Of course your chip has restrictions as well. (It max's out at 20 mhz).

If you have a 16mhz crystal, you might give it a try while you wait for a 20mhz to come in. 38400 baud works with debug out at 8 mhz, so at 16mhz I figure your 57600 might work. In the meantime, you could connect the gps to a max232 device, and change the baud lower with your computer. Then you could connect it to your pic at a lower baud rate, using a lower speed crystal. But 20mhz is highly recommended.

[mbox]

Hi,
Finally I manage to make the baudrate to 9600 with this guide http://docs.trenz-electronic.de/GlobalT ... ket_01.pdf but I have not connected it yet to PIC16F877A.
I'm going to use SERIN on PortB.0 to fetch data from GPS using 4Mz crytsal....feed back you later the result when I get back home.

regards,
mbox

[mbox]

Hi, I got a follow up question, I need to get latitude and longitude from this string
$GPRMC,053740.000,A,250.6319,N,12136.0099,E,2.69,7 9.65,100106,,,A*53. How can I achieve it using SERIN?

thanks,
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[mackrackit]

You would be better off using SERIN2.
Here is a snippet from something .

SERIN2 PORTB.2,16572,[WAIT("$GPGGA"),WAIT(","),DEC2 H,DEC2 M,DEC2 S,_
        WAIT(","),DEC2 ND,DEC2 NM,WAIT("."),DEC3 NMD,WAIT(",N,"),_
        DEC3 WD,DEC2 WM,WAIT("."),DEC3 WMD]

[mbox]

You would be better off using SERIN2.
Here is a snippet from something .

SERIN2 PORTB.2,16572,[WAIT("$GPGGA"),WAIT(","),DEC2 H,DEC2 M,DEC2 S,_
        WAIT(","),DEC2 ND,DEC2 NM,WAIT("."),DEC3 NMD,WAIT(",N,"),_
        DEC3 WD,DEC2 WM,WAIT("."),DEC3 WMD]

Hi, I'm trying to understand SERIN2 command. why this code do not work when I entered "hello"?

Include "modedefs.bas"
main:
Serin2 PORTC.7, T9600, error, [WAIT("hello")]
serout2 PortC.6, T9600, ["Valid"]
goto main

error:
serout2 PortC.6, T9600, ["Invalid"]
goto main
end

regards,
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[flotulopex]

Be careful while using TIMEOUT - you may get fuzzy results.

Have a look here http://www.picbasic.co.uk/forum/show...1443#post91443.

[mbox]

Be careful while using TIMEOUT - you may get fuzzy results.

Have a look here http://www.picbasic.co.uk/forum/show...1443#post91443.

Hi, thanks for the tip, it sure did saved me from trouble

regards,
mbox