How to Serial comm. wait for a string?

[Heckler]

Hi elcrcp,

If you look in the PBP manual under "serin2" you will find the "input modifiers" table...

DEC{1...10} allows you to specify how many decimal digits to receive into the next variable.
So DEC2 latdeg,DEC2 latmin,wait(".")
will receive the next 2 decimal digits into the variable "latdeg" and then the following 2 decimal digits into "latmin"

There is also a "SKIP n" parameter to ignore the next "n" digits, etc. etc.

GPRMC VAR BYTE[64]

hh      VAR BYTE  'hours
mm      VAR BYTE  'minutes
ss      VAR BYTE  'seconds
sss     var word  'milliseconds
fix     VAR WORD  'GPS fix
latdeg  VAR BYTE  'degrees latitude
latmin  VAR BYTE  'minutes latitude  
latminn var word  'fractional minutes latitude
NS      VAR BYTE  'north or south
londeg  VAR BYTE  'degrees longitude
lonmin  VAR BYTE  'minutes longitude
lonminn var word  'fractional minutes longitude
EW      VAR BYTE  'east or west
Knots   VAR byte  'speed in knots (units)
Knotss  var byte 'speed in fractional knots
course  var word  'heading
dy      VAR BYTE  'day
mt      VAR BYTE  'month
yr      VAR BYTE  'year

above is how I defined my varialbes...

so if the latdeg value is between 0-255 it will fit within the "byte" sized variable even if it is 1,2 or 3 digits (ie 99, 127, 08, etc)

PS. I may not have correctly sized all the varibles (bit, byte or word) so use your own judgment there... I wrote that code a couple of years ago.

Since "course" could be anything between 0-359 degrees it would need to be bigger than a byte as a byte can only hold up to 255

hope that helps

[Art]

Because you are typing, there will always be an enter character to terminate the string,
so you only need to fill a buffer, and check each byte for the enter character,
then you have all the time in the world for the program to look at the string
rather than trying to figure out what is going on in-between each byte being sent.

Same with GPS, I prefer to fill a buffer with the entire command, and count two bytes after the * char is received,
then look into the content after the entire sentence is received.

[flotulopex]

Hi,

This is the way time can be read "on the fly" from a serial GPS receiver module like this one

GPGGA_Time:
   SERIN2 GPSfrom,GPSbps,[WAIT("$GPGGA,"),STR GPS_D\6]
   LCDOUT $FE,2,GPS_D(0),GPS_D(1),":",GPS_D(2),GPS_D(3),":",GPS_D(4),GPS_D(5)
GOTO MAIN:

The PIC is waiting for the string $GPGGA, from the GPS module to arrive, then it fills an array with the 6 next incoming characters and displays them.

[Art]

Oh my, you’ll have a bunch of unneeded checking when the sentence could have been discarded for no fix or bad checksum.
Some GPS modules also put out a bad but valid time from their battery clocks until a position fix is acquired.
Not good if you were logging for a security system or something like that.

The thread isn’t necessarily about GPS, but it’s more or less the same thing.
You might has well make use of the UART if it’s present.

set a character counter to zero

charbuffer var byte[60]
character var byte
charcount var byte
charcount = 0

receive the serial with hserin with the smallest possible timeout so it will only give you a character if one is present in the buffer

‘pseudocode

hserin [character,lowesttimeout,timeoutlabel]
charbuffer[charcount] = character
charcount = charcount + 1

if character = enter or linefeed, etc. then
gosub investigate’ investigate the complete sentence and reset charcount
endif

timeoutlabel: