VAL Avionics COM 2000 Installation And Operator's Manual - page 24
V A L A V I O N I C S L T D
I N S 4 2 9 I N T E G R A T E D N A V I G A T I O N S Y S T E M
I N S T A L L A T I O N A N D O P E R A T O R ’ S M A N U A L
Revision 4
Page 24 of 30
December 2013
9.5
Message Formats
All messages will conform to the NMEA 0183 proprietary message format as follows. All characters will
be standard ASCII characters. No binary data characters will be used.
“$” .....................................Start of message character, ASCII “$” (024h)
“P”.....................................Proprietary message identifier
“MRR” ..............................II Morrow company identifier
c.........................................Message class identifier. Used to identify a message as either a
COMM of VHF NAV message. The COM 2000 can accept either the
“V” or “C” message command to facilitate operation as a stand alone
unit or as part of a emulated SL 30 unit.
nn ......................................Message identifier, two-digit number in ASCII characters.
d…d ..................................Message data characters defined for each message.
chksum ..............................Message checksum, including message identifier through data
characters. The two-digit checksum is generated by adding all values
of valid characters together, ignoring carry (if any). This value is
converted into two encoded hex
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characters (30h-3Fh).
The maximum message length, including the start of message character (“$”) and the end of message
This message format is the same as is used in the INS 429 / NAV 2000 / NAV 2KR. The COM 2000 /
COM 2KR will be able to accept all messages intended for a INS 429 / NAV 2000 / NAV 2KR without
generating a serial communications error. It will ignore all of those messages.
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Encoded Hex: each character consists of 4 bits of data placed in the low order nibble +30h. For example, the 8-bit
value of 5Fh would be encoded as two characters with values of 35h and 3Fh, which map to the ASCII characters
“5” and “?” respectively.