IDEC DS2_Series - Manual (Page 31)

DS2 series Instruction manual
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7. AREAscan TM DS2 SERIES – COMMUNICATION PROTOCOL
7.1. Packet description
As mentioned, the communication protocol requires a master unit and a slave unit. The
communication type is half duplex (RS485).
The exchange of information is made in the request-reply mode: the master sends a data packet to
the slave that replies sending another data packet to the master.
7.1.1 Binary data packet structure
A binary data packet is composed of a group of bytes placed in a well-defined sequence, that
identifies it univocally. It presents a heading, body and an end.
The heading and the end have a fixed length while the body has a variable length.
Packet start Length Type Data Packet end Checksum
• Packet beginning: 1 byte, STX ASCII code (‘0x02’)
• Length:
1 byte, length in bytes of the Type field plus the Data field
• Type: 1 byte, code identifying the packet type ( ‘A’, ‘B’, ‘C’ ASCII code, etc.)
• Data: variable number of bytes (from 0 to 254) that form the packet information
• Packet end: 1 byte, ETX ASCII code(‘0x03’)
• Checksum: 1 byte, complement to one of the Length, Type and
Data field bytes sum.
7.1.2. Short protocol binary data packet structure
There is a binary data packet with reduced protocol composed by one byte. This format is reserved
to trasmission of numeric type value only (for example one measure).
Data
Data: 1 byte with binary data packet
7.1.3. ASCII data packet structure
An ASCII data packet is composed of:
Packet start Type Data Packet end
• Packet beginning: 1 byte, ‘*’ ASCII code (0x2A)
• Type: 1 byte, code identifying the packet type ( ‘A’, ‘B’, ‘C’ ASCII code, etc.)
• Data: variable number of ‘0’-‘9’ ‘A’-‘Z’ ASCII codes (from 0 to 254) that form the
packet information
• Packet end: 1 byte, CR ASCII code (0x0D)
Heading Body End
Body
Heading Body End