ACR Electronics 2680 Product Support Manual page 17

5.4.1 VDM Message Format
!--VDM,x1,x2,x3,a,s--s,x*hh<CR><LF>
field 1 2 3 4
Field Format
1 x
2 x
3 x
4 a
5 s---s
6 x
NOTE 1 The length of an ITU-R M.1371 message may require the transmission of multiple sentences. The first
field specifies the total number of sentences used for a message, minimum value 1. The second field
identifies the order of this sentence in the message, minimum value 1. These cannot be null fields.
NOTE 2 The Sequential message identifier provides a message identification number from 0 to 9 that is
sequentially assigned and is incremented for each new multi-sentence message. The count resets to 0
after 9 is used. For a message requiring multiple sentences, each sentence of the message contains
the same sequential message identification number. It is used to identify the sentences containing
portions of the same message. This allows for the possibility that other sentences might be interleaved
with the message sentences that, taken collectively, contain a single message. This shall be a null field
for messages that fit into one sentence.
NOTE 3 The AIS channel is indicated as either "A" or "B". This channel indication is relative to the operating
conditions of the AIS unit when the packet is received. This shall be a null field when the channel
identification is not provided. The VHF channel numbers for channels "A" and "B" are obtained by using
a "query" (See IEC 61162-1, clause 5.3.2) of the AIS unit for an ACA sentence.
NOTE 4 This field supports a maximum of 62 valid characters for messages transferred using multiple
sentences, and 63 valid characters for messages using a single sentence.
NOTE 5 This cannot be a null field. See "x4" in 5.3.3.
5.4.2 VDM Message Types
For example, the information contained in the s - - s portion of the VDM = Encapsulated ITU-R M.1371 radio
message. Note that messages 5 and 19 may be sent as multi part messages using the x1, x2 and x3
parameters for message sequence control.
VDL Message number
AIS Target Display Information
1, 2, 3, 9,18, 21
4
5*
19*
Safety message handling
12
14
External Application
handling
6
8
5 6
Description
Total number of sentences needed to transfer the message
1
Sentence number , 1 to 9
Sequential message identifier
3
AIS Channel, "A" or "B"
Encapsulated ITU-R M.1371 radio message
5
Number of fill-bits , 0 to 5
VDM Message description
position report
base station report
voyage related data
Class B – extended data
addressed safety related
broadcast safety related
binary addressed
binary broadcast
2
, 0 to 9
4
17 of 25
1
, 1 to 9
Y1-03-0222 Rev T4T4