ACR Electronics ACR-AIS-300 Manual De Usuario

 

 

17 of 25 

Y1-03-0222 Rev T4T4  

 5.4.1 

VDM 

Message 

Format 

 !--VDM,x1,x2,x3,a,s--s,x*hh<CR><LF> 
 

field   1  2  3 4    5 6 

 

1 

x 

Total number of sentences needed to transfer the message

1

, 1 to 9 

2 x 

Sentence 

number

1

, 1 to 9 

3 

x 

Sequential message identifier

2

, 0 to 9 

4 

a 

AIS Channel, "A" or "B"

3

 

5 

s---s 

Encapsulated ITU-R M.1371 radio message

4

 

6 

x 

Number of fill-bits

5

, 0 to 5 

 
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. 
 

AIS Target Display Information 
1, 2, 3, 9,18, 21 

position report 

4 

base station report 

5* 

voyage related data 

19* 

Class B – extended data 

Safety message handling 
12 

addressed safety related 

14 

broadcast safety related 

 

6 binary 

addressed 

8 binary 

broadcast