COBHAM Messenger Portable Decoder, User Manual

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100-M0081X1 16 of 29
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Command Format
SYNH ID LENH LENL CMD DATA SUM SYNE
1B 2B 1B 1B 1B (LENH/LENL)B 1B 1B
0xAA ID number
of the
connected
MPD Length of
(CMD+DATA)
In unit of Byte Command
Code N Bytes of
optional DATA Sum of
(ID,LENH,
LENL,CMD,DAT
A) 0x55
Acknowledge Format
SYNH ID LENH LENL ACK DATA SUM SYNE
1B 2B 1B 1B 1B (LENH/LENL)B 1B 1B
0xAA ID number
of the MPD
Length of
(ACK+DATA)
In unit of Byte Acknowledg
e Code N Bytes of
optional DATA Sum of
(ID,LENH,
LENL,ACK,DATA) 0x55
Warning Format
SYNH ID LENH LENL WARN DATA SUM SYNE
1B 2B 1B 1B 1B 4B or 1B 1B 1B
0xAA ID number
of the MPD Length of
(WARN+DATA),
In unit of Byte
Warning
Code
0x11 4 or 1 bytes of
DATA Sum of
(ID,LENH,
LENL,WARN,DAT
A) 0x55
Definition of Data Segment
Data
Segm
ent
Definition and Explanation
SYNH
Sync. flag is 0xAA.
ID
ID number for each MPD. The monitoring program should use the right ID number to
communicate with the corresponding MPD. ID=0x0000 refers to one reserved ID, and the
monitoring program can use ID=0x0000 to communicate with any one of MPD.
LENH Data length
high byte LENH and LENL form one 16bit unsign integer. It represents the DATA length,
the unit is in byte. When there is no data, the value is 0.
LENL
Data length
low byte
CMD Command code, which refers to the command that the monitoring program sends to MPD.
ACK Acknowledge code, which refers to the acknowledge that MPD sends to the monitoring program.
When the command is successfully executed, ACK=CMD, or otherwise, ACK=0x00.
WAR
N Warning code, which refers to the warning that MPD initiatively sends to the monitoring
program. Its value is always 0x11.
DATA In Command or Acknowledge frame, it is an optional item, and its length is changeable. In
Warning frame, it shows 4 or 1 byte warning information.
SUM
Check summary
，
which is the byte summary of LENH, LENL, CMD/ACK, DATA, carry omitted.
SYNE Sync. End, total is 0x55.