Danfoss VLT Series Design Manual page 140

7. RS-485 Installation and Set-up
7.4.2. Message Structure
Each telegram begins with a start character (STX)=02 Hex, followed by a byte denoting the mes-
sage length (LGE) and a byte denoting the adjustable frequency drive address (ADR). A number
of data bytes (variable, depending on the type of telegram) follows. The telegram is completed
by a data control byte (BCC).
7.4.3. Message Length (LGE)
The message length is the number of data bytes plus the address byte ADR and the data control
byte BCC.
7
The length of telegrams with 4 data bytes is
The length of telegrams with 12 data bytes is
The length of telegrams containing texts is
1) The 10 represents the fixed characters, while the "n" is variable (depending on the length of
the text).
7.4.4. Adjustable Frequency Drive Address (ADR)
Two different address formats are used.
The address range of the adjustable frequency drive 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 = Adjustable frequency drive address 1-31
2. Address format 1-126:
Bit 7 = 1 (address format 1-126 active)
Bit 0-6 = Adjustable frequency drive address 1-126
Bit 0-6 = 0 Broadcast
The slave returns the address byte unchanged to the master in the response telegram.
7.4.5. 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.
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VLT ® HVAC Drive Design Guide
LGE = 4 + 1 + 1 = 6 bytes
LGE = 12 + 1 + 1 = 14 bytes
1)
10 +n bytes