Fc Protocol Message Framing Structure - Danfoss VLT HVAC Drive FC 100 Instruction Manual

VLT HVAC Low Harmonic Drive Instruction
Manual

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 Message Structure
Each message begins with a start character (STX)=02 Hex, followed by a byte denoting the message length (LGE) and a byte denoting the adjustable
frequency drive address (ADR). A number of data bytes (variable, depending on the type of message) follows. The message 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.
The length of messages with 4 data bytes is
The length of messages with 12 data bytes is
The length of messages 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
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7 RS-485 Installation and Set-up
LGE = 4 + 1 + 1 = 6 bytes
LGE = 12 + 1 + 1 = 14 bytes
1)
10 +n bytes
7
7-5