GPS -- NMEA Input & Parsing

PJAllen · 2005-09-19 00:03

Here's a sample of the NMEA sentence that I'm dealing with:
$GPGLL,3330.6092,N,11200.6777,W,202110.595,A*27
All I want is the stuff in RED.·

I haven't tried it before, but I used STR to capture it all, using SKIPs, and more STRs.· At the end I read it out to a LCD.
I don't know if I'm writing the input with the STR right.· I have the feeling that I can't use it and then re-use it without the pointer being re-set, too.· The resulting output to the LCD basically repeats all three lines.··
My GPS is outputting the $GPGLL sentence once every 5 seconds.· I push the button to initiate the process: it waits to get/receive a "GLL,", then it starts a grab, then it goes to the printout and my LED comes on, I get the printout on the LCD, the LED goes out, and then it goes back to the top for another button push.
The characters that I get back are odd-ball.

Am I taxing the formatting ability of the BS2 at 4800?· Is my use of STR incorrect?· Any constructive criticism?
·
Here is my programme --

BtnWrk  VAR Byte
CD VAR Byte  (25)'co-ordinate data

Prelims:
   DIRS = $0F        'MSB INs, LSB OUTs
   OUTL = %10000000  'preset OUTs
   INH  = %00000000  'preset INs; button bit0,
Push:
   BUTTON 8,1,255,20,BtnWrk,1,Rtrv
   GOTO Push
Rtrv:
   SERIN 9, 188,[noparse][[/noparse]WAIT("GLL,"),STR CD\7] 'ddmm.mm
   SERIN 9, 188,[noparse][[/noparse]SKIP 3,STR CD\1]       'skip 3&4 decpl,comma; take N
   SERIN 9, 188,[noparse][[/noparse]SKIP 1,STR CD\8]       'dddmm.mm
   SERIN 9, 188,[noparse][[/noparse]SKIP 3,STR CD\1]       'skip 3&4 decpl,comma; takeW
   SERIN 9, 188,[noparse][[/noparse]SKIP 1,STR CD\6]       'skip comma; take hhmmss
   SERIN 9, 188,[noparse][[/noparse]SKIP 5,STR CD\1]       'skip time decpl, comma; a/v Status
Got1:
   OUTL=%10000001            'LED=ON, gonna printout; serout bit HI for NO NUL
   SEROUT 7, 188, [noparse][[/noparse]$0c]      'form feed
   SEROUT 7, 188, [noparse][[/noparse]STR CD\8] 'ddmm.mmN
   SEROUT 7, 188, [noparse][[/noparse]$0A,$0D]  'LF,CR
   SEROUT 7, 188, [noparse][[/noparse]STR CD\9] 'dddmm.mmW
   SEROUT 7, 188, [noparse][[/noparse]$0A,$0D]  'LF,CR
   SEROUT 7, 188, [noparse][[/noparse]STR CD\7] 'hhmmssA
   OUTL=%10000000            'LED=OFF, endof printout; serout bit HI for NO NUL
   GOTO Push

Post Edited By Moderator (Chris Savage (Parallax)) : 9/19/2005 12:02:22 AM GMT

Jon Williams · 2005-09-19 01:16

Part of the problem is that you're breaking the input into lots of SERIN statements that take time to load up and get ready.· You should try to capture it in one (long) instruction.

· ·SERIN GPS, Baud, [noparse][[/noparse]WAIT("GPGLL,"
···················· DEC latD, SKIP 1, DEC latM,
···················· DEC lonD, SKIP 1, DEC lonM, SKIP 1,
···················· DEC2 hrs, DEC2 mins, DEC2 secs,
···················· SKIP 5,·status]

If you do a bit of search you'll find I've posted a bunch of GPS related programs that you can work with.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

PJAllen · 2005-09-19 02:00

·
···

·· I found·much the same·-- sure looks good to me:

BtnWrk  VAR Byte
LA VAR Byte  (7)
NS VAR Byte  (1)
LO VAR Byte  (8)
EW VAR Byte  (1)
TM VAR Byte  (6)
AV VAR Byte  (1)
Prelims:
   DIRS = $0F        'MSB INs, LSB OUTs
   OUTL = %10000000  'preset OUTs
   INH  = %00000000  'preset INs; button bit0,
Push:
   BUTTON 8,1,255,20,BtnWrk,1,Rtrv
   GOTO Push
Rtrv:
   SERIN 9,188,[noparse][[/noparse]WAIT("GLL,"),STR LA\7,SKIP 3,STR NS\1,SKIP 1,STR LO\8,SKIP 3,STR EW\1,SKIP 1,STR TM\6,SKIP 5,STR AV\1] 'ddmm.mm
Got1:
   OUTL=%10000001            'LED=ON, gonna printout; serout bit HI for NO NUL
   SEROUT 7,188,[noparse][[/noparse]$0c]        'form feed
   SEROUT 7,188,[noparse][[/noparse]"   GPS BY PJALLEN",$0A,$0D]
   SEROUT 7,188,[noparse][[/noparse]STR LA\7]   'ddmm.mm
   SEROUT 7,188,[noparse][[/noparse]$04]        'RC
   SEROUT 7,188,[noparse][[/noparse]STR NS\1]     'N
   SEROUT 7,188,[noparse][[/noparse]$0A,$0D]    'LF,CR
   SEROUT 7,188,[noparse][[/noparse]STR LO\8]   'dddmm.mm
   SEROUT 7,188,[noparse][[/noparse]$04]        'RC
   SEROUT 7,188,[noparse][[/noparse]STR EW\1]   'W
   SEROUT 7,188,[noparse][[/noparse]$0A,$0D]
   SEROUT 7,188,[noparse][[/noparse]"UTC ",STR TM\6]
   SEROUT 7,188,[noparse][[/noparse]$04,$04,$04]'RCx3
   SEROUT 7,188,[noparse][[/noparse]STR AV\1]   'A
   OUTL=%10000000            'LED=OFF, endof printout; serout bit HI for NO NUL
   GOTO Push

First, it hit me: I need to call the STRs by different names

.· I got a little further·doing that.· Then, YES, as you Reply'd, Jon, I needed to write my capture as one line; that made the Sun to shine.· Now, I'll re-program the GPS to have it·send the sentence every 2 seconds, I think that's as fast as she goes.· I'll·also take out the test button and those instructions --·but I'm keeping the LED.

PJAllen · 2005-09-19 23:18

I decided to parse a little more, so that I wasn't collecting the decimal points and was thereby able to pick up the 3rd decimal place for both the latitude and longitude.· Further, on the LCD, I placed the N/S and E/W before their readings and additionally formatted to·insert "deg" and "min" to make it easier to read. [noparse][[/noparse]Also, no more "ready to sample" button.]

By the way, I'm using a 4 x 20 LCD from a previous, unrelated, project.· It has an EIA-232 input.·
My BS2 is a "HomeWork Board" and I use a MAX232 driver between its I/O and the LCD and the GPS.

' {$STAMP BS2}
' {$PBASIC 2.0}
' {$PORT COM1}
BtnWrk  VAR Byte
PA VAR Byte (2)
PM VAR Byte (2)
PD VAR Byte (3)
NS VAR Byte (1)
MA VAR Byte (3)
MM VAR Byte (2)
MD VAR Byte (3)
EW VAR Byte (1)
TM VAR Byte (6)
AV VAR Byte (1)
Prelims:
   DIRS = $0F        'MSB INs, LSB OUTs
   OUTL = %10000000  'preset OUTs
   INH  = %00000000
PrepCUR:
   SEROUT 7,188,[noparse][[/noparse]$0c,$19,$00]  'form feed, blank cursor
Rtrv:
   SERIN 9,188,[noparse][[/noparse]WAIT("GLL,"),STR PA\2,STR PM\2,SKIP 1,STR PD\3,SKIP 2,STR NS\1,SKIP 1,STR MA\3,STR MM\2,SKIP 1,STR MD\3,SKIP 2,STR EW\1,SKIP 1,STR TM\6,SKIP 5,STR AV\1]
LCD:
   OUTL=%10000001            'LED=ON, gonna printout; serout bit HI for NO NUL
   SEROUT 7,188,[noparse][[/noparse]$02," * GPS BY PJALLEN *",$0A,$0D]
   SEROUT 7,188,[noparse][[/noparse]STR NS\1,"  ",STR PA\2,"deg ",STR PM\2,".",STR PD\3,"min"]
   SEROUT 7,188,[noparse][[/noparse]$0A,$0D]    'LF,CR
   SEROUT 7,188,[noparse][[/noparse]STR EW\1," ",STR MA\3,"deg ",STR MM\2,".",STR MD\3,"min"]
   SEROUT 7,188,[noparse][[/noparse]$0A,$0D]
   SEROUT 7,188,[noparse][[/noparse]"UTC ",STR TM\6]
   SEROUT 7,188,[noparse][[/noparse]"        ",STR AV\1]
   OUTL=%10000000            'LED=OFF, endof printout; serout bit HI for NO NUL
   GOTO Rtrv

GPS -- NMEA Input & Parsing

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