Fc Protocol Message Framing Structure - Fc 300 - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

FC Protocol Message Framing Structure - FC 300

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.
Telegram Structure
Each telegram begins with a start character (STX)=02 Hex, followed by a byte denoting the telegram
length (LGE) and a byte denoting the frequency converter address (ADR). A number of data bytes (var-
iable, depending on the type of telegram) follows. The telegram is completed by a data control byte
(BCC).
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).
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
Bit 0-6 = 0 Broadcast
The slave returns the address byte unchanged to the master in the response telegram.
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.
RS-485 Installation and Set-up
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MG.33.B8.02 - VLT is a registered Danfoss trademark
LGE = 4 + 1 + 1 = 6 bytes
LGE = 12 + 1 + 1 = 14 bytes
10 1) +n bytes
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