Campbell CR23X, Руководство оператора

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APPENDIX B. CONTROL PORT SERIAL I/O INSTRUCTION 15
B-8
DTR DSR/DCD
DSR/DCD DTR
RTS CTS
CTS RTS
TXD RXD
RXD TXD
GND GND
B.5.2 DATA BUFFERING
Since P15 is executed in a program table at
fixed intervals (i.e. 60 seconds), it is possible to
miss data transmitted from a sensor if the
sensor outputs data automatically at a different
interval (i.e., 10 seconds). P15 will support
buffering of this data up to the maximum
number of characters specified in parameter 8
minus 1 data byte. For example: if your
application requires that 15 data bytes be
buffered, make Parameter 8 equal to 16. If
parameter 2 is indexed (--) no data buffering will
occur.
B.6 INPUT DATA FILTERS.
P15 supports search filters strings that can be
applied to a received data set. It is typically
used locate the beginning of the desired data
set. Multiple filters can be applied if the data is
imbedded in a long string. To implement a filter
string follow P15 immediately with either
instructions P63 or P68 (both of which are
extended parameter instructions). Multiple use
of these instructions can be used if the search
string is longer than 8 characters. Separate
different types of filter strings with a null
character (00). Once the first string has been
found and the data decoded and loaded into
input locations the next sequential string loaded
into P63 or P68 (after the 00) will be used for
any other incoming data. If the filter string is not
found -99999 will be stored in the input location.
Once the last string has been found and the
data decoded and loaded into input locations,
the first string loaded will be used again.
Enter the actual filter/search string by keying the
decimal equivalent of the ASCII character (see
Appendix E. of the CR23X Operators Manual).
Example: GPS receiver program
A common application with P15 is to read in
data from a GPS receiver. The GPS receivers
typically have a defined serial output protocol
called NMEA 0183. NMEA 0183 is an interface
protocol created by the National Marine
Electronics Association (http://www.nmea.org/).
The NMEA 0183 Standard defines electrical
signal requirements, data transmission protocol,
timing and specific sentence formats for a 4800
baud serial data bus.
The primary advantage of this data string when
used with P15 is that data is separated with
commas. Since P15 only interprets and decodes
numerical values the commas are treated as data
delimeters resulting in each navigation value
residing in a unique input location.
Two common message strings that come out of
GPS receivers are the GGA and VTG
messages. The GGA message includes time,
position and fix related data for the GPS
receiver. The VTG message conveys the
actual track made good and the speed relative
to the ground. Example are listed below.
EXAMPLES:
GGA Position String - 63 characters
including CRLF
$GPGGA,174548,4146.008,N,11151.240,W,1,6
,001.9,1113,M,-017,M,,*40CRLF
Field Data Description
1. $GPGGA message identification
2. 174548 UTC of position (i.e.,
Greenwich mean Time)
3. 4146.008 Latitude
4. N N (North) or S (South)
5. 11151.240 Longitude
6. W W (West) or E (East)
7. 1 GPS Quality Indicator:
0=No GPS Available,
1=GPS Available,
2=DGPS
8. 6 Number of Satellites in use
9. 001.9 Horizontal Dilution of
Precision (HDOP).
10. 1113 Antenna Altitude
11. M M = Meters
12. -017 Geoidal Separation in Meters.
13. M M = Meters
14. *40 Checksum
15. CRLF Carriage Return Line
Feed