rs232

[rondo2]

hi ive connected a gps unit up direct to my serial port via a max232 chip

but i'm only seeing the nmea string when i toggle the power on and off to the rs232 chip, anyone have any idea why this is

i'm using the attached schematic

i did have the unit connected to a pic micro waiting for a particular nmea string so i could parse it but the pic wasn't seeing anything, so thought i would connect it directly to the serial port just to see if its outputting anything

[mackrackit]

I missread that. Do not use an inverter chip with the gps.
It is not needed with the PC and post your code too.

[ScaleRobotics]

Oops, This is assuming you mean that you are connecting your gps to your PIC chip, and not your computer. If you are just connecting your gps to your computer, no need for a max232 chip.

I've used the max232 chip with gps before. If you are using a standard GPS to PC serial cord, you will need to either swap your wires 7 and 8 on the max232 chip, or insert a null modem adapter on your gps cable.

[rondo2]

hi

sorry if my original post was confusing i typed it in a rush lol


first of all i connected my gps unit directy to a pic micro then using serin2 and wait, i waited for a particular nmea sentence to parse it etc, and the pic was just waiting it never could see even a $ sign coming from the gps unit,

so then...

got rid of the pic and i connected the gps unit directly to my pc's serial port via an rs232 chip, and viewed the data via microcode studio serial communicator

but the data would only be sent to the pc when i applied and removed power to the rs232 chip repeatedly if that makes sense.


below is the basic code i created just to see if the gps unit was transmitting data to the pic.

 @ device  pic16f870,WDT_OFF            'Watch Dog Timer Disabled
 @ device  pic16f870,PROTECT_OFF        'Code Protect Off
 @ device  pic16f870,XT_OSC             'Using External Oscillator
 @ device  pic16f870,BOD_on            'Brown Out Timer Disabled 
 @ device  pic16f870,PWRT_on          'Power On Timer Disabled
 @ device  pic16f870,LVP_OFF            'Low Voltage Programmed Disabled




define OSC 20

'TRISA = %11111111 
'TRISC = %00000000

'ADCON0.0=0
'ADCON1=7 ' ALL PINS SET TO DIGITAL


'Pin Assignments


GPIO0 VAR PORTA.0
NC VAR PORTA.4
TX var portb.5
RX VAR PORTA.2
Reset var porta.1
GPIO4 var porta.5  

'Variables

gps_data var byte


HIGH PORTC.0
PAUSE 200
LOW PORTC.0
PAUSE 200

SEROUT2 PORTC.1,16468,["GPS TEST$123456"]

pause 500 'allow gps module to init





'if gpio4=0 then high portc.3'(red)


reset_unit:

low reset

pause 100

high reset


MAIN:


serin2 TX,16468,[WAIT("$GPGGA"),str gps_data\6]



PAUSE 200

HIGH PORTC.0
PAUSE 200
LOW PORTC.0
PAUSE 200

SEROUT2 PORTC.1,16468,[str gps_data\6]

GOTO MAIN

[mackrackit]

Sounds about right for the PC, data getting through as the
232 chip was powering up and down.
232 chip is not needed with the PC and if you are
using SERIN2 then run the PIC in inverted mode.
Keep it simple...

[rondo2]

Sounds about right for the PC, data getting through as the
232 chip was powering up and down.
232 chip is not needed with the PC and if you are
using SERIN2 then run the PIC in inverted mode.
Keep it simple...

are you talking about communicating from the pic to the pc, in this instance i was not using a rs232 chip, but when soley connecting the gps unit directly to the serial port i was using a rs232 chip if i bypassed the chip i just got garbage on the screen.

[mackrackit]

Now I think I may see the problem. I will assume your GPS unit sends data at 4800?
Here is a snippet from one of my programs. No 232 chip.

SERIN2 PORTB.1,16572,[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]

[ScaleRobotics]

gps_data var byte

serin2 TX,16468,[WAIT("$GPGGA"),str gps_data\6]

Your gps_data is defined as a single byte. You want an array to work with, so you should define it as something like:

gps_data var byte[6]

[rondo2]

Your gps_data is defined as a single byte. You want an array to work with, so you should define it as something like:

gps_data var byte[6]

hi thanks for pointing that out but still nothing.

i changed my code to serin2 TX,84,[WAIT("$GPGGA"),WAIT(","),DEC2 H,DEC2 M,DEC2 S]


PAUSE 200

HIGH PORTC.0
PAUSE 200
LOW PORTC.0
PAUSE 200

SEROUT2 PORTC.1,16468,[dec2 H, dec2 M, dec2 S]

GOTO MAIN

still nothing

the gps module is connected properly it is receiving 3.3v so unsure whats going on

do you no if it must have a backup battery, because at the moment i don't have that pin connected to anything

[ScaleRobotics]

What's your hardware setup? Got a picture? Can you show the whole code? I wonder what your TX pin is doing with the serial in, but I can't tell from here.

The code you just posted is not inverted, so I assume you have the max232 back in?