CDR Series
Installation Instructions
14
Table 2 - Header Bit Format
Field
Bit
Meaning
When Cleared
When Set
Command 7
Message Type
Simple Command Format Special Command Format
Table 1 - Message Format
Type
Value
Start Marker
0x02
Address
RS485 Address
Command
See Table 2, Table 3 and Table 4
Data Field 1
See Table 2, Table 3 and Table 4
Data Field 2
See Table 2, Table 3 and Table 4
Data Field 3
See Table 2, Table 3 and Table 4
Checksum
Arithmetic value of all preceding values to make the
line up to zero
End Marker
0x03
RS485 MENU CONTROL
Command Format
The RS485 camera commands consist of a six-byte data stream for all functions comprising
of the information shown in Table 1 below:
Start Marker
- This value marks the start of the data packet. It will always be 0x02 (ASCII
STX) and will always be the first recognised byte for the message packet. Since all the
messages packets are of fixed length, there is no requirement for a length byte.
Address
- This byte contains the destination node for the command packet. A camera will
only accept commands intended for it. A camera will become active on receipt of its address,
and will remain active until receipt of a complete command.
Command
- The Command byte contains a bit that determines whether the values in the
succeeding fields refer to simple control functions or special commands. When sending
simple control commands, the Commands and Data 1 fields are combined as two Command
fields to provide the complete message.
Table 3 lists the usage of the bits within the basic command format, whereas Table 4 shows
the commands for other control functions.
Checksum
- This is the arithmetic sum from the following equation. It makes the entire line
equate to zero for validation purposes.
Camera A C Data Field 1 + Data Field 2 + Data Field 3 = Checksum
End Marker
- This value marks the end of the message packet and will always occur in this
location in the message stream. The Value will always be 0x03 (ASCII ETX).
