Fc Protocol Message Framing Structure - Danfoss VLT Series Design Manual

7. RS-485 Installation and Set-up

7.4. FC Protocol Message Framing Structure

7.4.1. Content of a Character (byte)
Each character transferred begins with a start bit. Then 8 data bits are transferred, corresponding
to a byte. Each character is secured via a parity bit, which is set at "1" when it reaches parity (i.e.
when there is an equal number of 1's in the 8 data bits and the parity bit in total). A character is
completed by a stop bit, thus consisting of 11 bits in all.
7.4.2. Telegram Structure
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Each telegram begins with a start character (STX)=02 Hex, followed by a byte denoting the tele-
gram length (LGE) and a byte denoting the frequency converter 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. Telegram Length (LGE)
The telegram length is the number of data bytes plus the address byte ADR and the data control
byte BCC.
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. 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
126
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VLT HVAC Drive Design Guide
LGE = 4 + 1 + 1 = 6 bytes
LGE = 12 + 1 + 1 = 14 bytes
10 1) +n bytes