Telegram Structure; Telegram Length (Lge); Frequency Converter Address (Adr); Data Control Byte (Bcc) - Danfoss VLT AutomationDrive FC 300 Design Manual

RS-485 Installation and Set...

10.6.2 Telegram Structure

Each telegram has the following structure:
1. Start character (STX)=02 Hex
2. A byte denoting the telegram length (LGE)
3. A byte denoting the frequency converter address
(ADR)
A number of data bytes (variable, depending on the type
of telegram) follows.
A data control byte (BCC) completes the telegram.
STX LGE ADR
Illustration 10.5 Telegram Structure

10.6.3 Telegram Length (LGE)

The telegram length is the number of data bytes plus the
address byte ADR and the data control byte BCC.
4 data bytes
12 data bytes
Telegramscontaining texts
Table 10.3 Length of Telegrams
1) The 10 represents the fixed characters, while the "n'" is variable
(depending on the length of the text).

10.6.4 Frequency Converter Address (ADR)

Two different address formats are used.
The address range of the frequency converter is either 1-31
or 1-126.
1. Address format 1-31:
Bit 7 = 0 (address format 1-31 active)
Bit 6 is not used
Bit 5 = 1: Broadcast, address bits (0-4) are not
used
Bit 5 = 0: No Broadcast
Bit 0-4 = frequency converter address 1-31
2. Address format 1-126:
Bit 7 = 1 (address format 1-126 active)
Bit 0-6 = frequency converter address 1-126
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®
VLT AutomationDrive FC 300 Design Guide, 0.25-75 kW
DATA BCC
LGE=4+1+1=6 bytes
LGE=12+1+1=14 bytes
1)
10 +n bytes
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MG33BE02 - VLT is a registered Danfoss trademark
Bit 0-6 = 0 Broadcast
The slave returns the address byte unchanged to the
master in the response telegram.

10.6.5 Data Control Byte (BCC)

The checksum is calculated as an XOR-function. Before the
first byte in the telegram is received, the Calculated
Checksum is 0.
10 10
183