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QuercusVL Programming Manual
information or to request an action (activate an output, reboot the unit, etc.). All requests will
be answered immediately by the unit with a response message with the information requested,
an ACK if the message did not expect a response, or a NAK if the message could not be
properly received, interpreted, or completed.
Please note that between the reception of a request and its response, an event can occur in
the system, so that the first message to arrive after a request has been made might not be the
response to the request.
Example of requests and their responses:
4.1. Message format
Messages will always have the same format; Bytes are ordered in all fields with the “little-
endian” system:
●
Stx (1 byte): byte that marks the start of a frame (ASCII character 2).
●
Unit Id (4 bytes): identifier of the capture unit sending or receiving the message; a zero
means that this field has to be ignored.
●
Size (4 bytes): total size of the message in bytes.
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Unit
Central System
Action
ACK (Action)
Get information
Information
Unknown message
NAK
ACK (Event)
Action
Event
Event
ACK (Action)
Type
Version
Size
Id
2
2
4
4
Variable
1
Stx
Etx
1
1
Bcc
UnitId
4
Message data