Advent Communications
209298 - DVE5000 Technical Operation Handbook - CL140042 Page 67 of 110
8.5. PACKET STRUCTURE
This product uses a non-printable packet format. This means that the full range of 255
ASCII characters can appear in the message.
The format of all messages is:
[STX] [BYTE COUNT] [ADDRESS] [DATA....] [CHECKSUM] [ETX]
STX (start of transmission)
STX is the ASCII character 2. It is one byte in size and is used to represent the start of each
message.
BYTE COUNT
The BYTE COUNT is one byte in size and is the total number of bytes in the packet, i.e.
number of data bytes plus five (one each for STX, BYTE COUNT, ADDRESS, CHECKSUM
and ETX).
ADDRESS
The ADDRESS is one byte in size. This is the address of the equipment to which the packet
is being sent. Unique addresses can be in the range 001 to 255.
DATA
This is the actual data being sent to the equipment. In any one packet, the maximum
number of data bytes is 250. The DATA section includes the remote command and any
associated parameters.
CHECKSUM
The CHECKSUM is one byte in size and is included for error detection. It is the modulo
addition of all ADDRESS and DATA bytes.
Here is a typical example calculation:
[STX] [BYTE COUNT] [ADDRESS] [DATA....] [CHECKSUM] [ETX]
[2][8] [97 98 99] [43] [3]
The checksum is calculated as follows:
CHECKSUM = (5 + 97 + 98 + 99) mod 256 = 43
ETX (end of transmission)
ETX is the ASCII character 3. It is one byte in size and is used to represent the end of each
message.
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