Serial line data
DIGI_NED can be used transmit data from the serial line to any of the configured output ports. DIGI_NED expects serial data in the form of "sentences". These are terminated ASCII lines. DIGI_NED will pick up selected lines based on the first characters in the line. DIGI_NED will transmit at regular intervals the latest received complete line of data.
With this DIGI_NED can send data from a GPS, Ultimeter or other devices connected via a serial line. You can sent multiple sentences if you want. DIGI_NED will automatically do a checksum-check if a checksum is present. Checksums terminate a "sentence" with "*xx" where "xx" is the hexadeximal sum. If the asterix is found in the third position before the end of the line DIGI_NED assumes a checksum is present.
The checksum is compared with an internally calculated checksum.
Sentences that fail will be ignored. The calculation follows the NMEA standard used for GPS devices among others. The checksum is an EXOR operation staring at the second character up to, but not including, the "*".
If no checksum is present the data is accepted as is. An examples of a start of a sentence is:
- For GPS : $GPRMC or $GPGGA
- For Ultimeter : $ULTW or !!
- For Directon finder: %
If the wanted type of sentence is not specified (empty line following the "serial:" rule) all the data on the serial input is accepted (if
it doesn't fail the checksum). Note that DIGI_NED will only output the most recently read complete line in this case. Normally DIGI_NED transmits a packet for every specified sentence, so if you specified "$GPRMC $GPGGA" then both the $GPRMC and $GPGGA sentence will be transmitted.
DIGI_NED will convert any control character on the serial line into a dot ".", except which is the line terminator and which is discarded.
The interface is always 8 bit, no parity, one stopbit. Accepted speeds are 1200, 2400, 4800 and 9600 baud. This covers the mutlitude of serial inputstreams, including NMEA. The interface uses hardware flowcontrol on send an receive. For a 3 wire connection shortcut RTS and CRS and shortcut DTR, DSR and DCD in the connector at the DIGI_NED side of the wire.
Software-flowcontrol (Xon/Xoff) is not used.