BLUEBOX Gen.2 HFM
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3
Communication Features
3.1
Introduction
There are two types of data packets used in the communication:
•
Outgoing data packets from the ‘master’ (PLC) to the ‘slave’ in order to
send a command or an answer to the
BLUEBOX
•
Incoming data packets to the ‘master’ (PLC) from the ‘slave’ (
BLUEBOX
)
carrying for example the answer to a command
In the following example, a buffer length of 16 bytes is supposed.
The outgoing data packets from the ‘master’ assume the following structure:
Header
1° Byte
2° Byte
Max 14 Byte
7
6
5
4
3
2
1
0
Length
Data
Req tx
Ack rx
More
The outgoing data packet consists of a header (first two bytes) and a data
buffer of 14 bytes.
The first byte of the header consists of the following flags:
•
Bit 7 … 3: Not used
•
Bit 2: More, set to ‘1’ means that the message is composed of several
data packets
•
Bit 1: Ack rx, reception acknowledge
•
Bit 0: Req tx, transmission request
The second byte (Length) of the header specifies the number of data bytes in
the data buffer (max 14 data bytes in this example).
