V A L A V I O N I C S L T D
N A V 2 0 0 0 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
Pre-Release Issue
Page 21 of 29
Sept. 2013
8.5 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. Those message types,
which are also supported by the VAL COM 2000 VHF
Transceiver, will use the “C” identifier to allow the NAV 2000
to accept COMM radio commands from existing products.
All other messages will use the “V” identifier to indicate that
they relate to a VHF NAV receiver.
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).
<CR> ................................ASCII carriage return (0Dh)
<LF> .................................ASCII line feed (0Ah)
The maximum message length, including the start of message character (“$”) and the end of
message <CR><LF> sequence, is 25 bytes.
This message format is the same as is used in the VAL COM 2000 VHF Transceiver. The NAV
2000 will be able to accept all messages intended for a COM 2000 without generating a serial
communications error. It will forward all of those messages.
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Encoded Hex: each character consists of 4 bits of data placed in the low order 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.
