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CoMMunICAtIon ProtoCoL
Communication Protocol
The DVR protocol uses packets based on the NMEA message format. This consists of an
ID, comma delimited fields, a checksum field and a two-character checksum. A response
message is transmitted from the DVR upon receiving a message. It will either be the specific
response for the command, a general DSACK response, or a DSNAK response if the com-
mand is not recognized or the packet is invalid.
Physical and Data Link Layer
The DVR communicates via RS232 or RS422 interface using the following port settings
(Table 11).
Package Message format
The NMEA (standard protocol) message format is an ASCII string that consists of a message
ID, comma delimited data fields and a checksum field. The message format is described in
Table 12.
LenGth
1
5
n
1
2
baUD Rate
Data bitS
PaRity
StaRt bitS
StoP bitS
fLoW ContRoL
VaLUe
DeSCRiPtion
'$'
Packet Message Start Byte
MSGID
Message Identifier; first two characters represents the manufac-
turer (DS); last three are Command Code
Comma Delim-
field 0, field 1, field n
ited fields
'*'
Checksum Delimiter Byte
Checksum
Checksum is two ASCII characters representing a hexadeci-
mal byte 00 to ff. Value is the exclusive or (Xor) of all bytes
between, but not including characters '$' and '*'
19200 bps
8
NONE
1
1
NONE
table 11
table 12
MPC-ML2DVR-UM(A) 3/2015
47
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