Fc Protocol Overview; Network Configuration; Fc Protocol Message Framing Structure - Danfoss VLT AQUA Drive FC 202 Design Manual

System Integration
3 3
Min. 200 mm
90° crossing
Illustration 3.43 Cable Routing

3.8.5 FC Protocol Overview

The FC protocol, also referred to as FC bus or standard
bus, is the Danfoss standard fieldbus. It defines an access
technique according to the master-slave principle for
communications via a serial bus.
1 master and a maximum of 126 slaves can be connected
to the bus. The master selects the individual slaves via an
address character in the telegram. A slave itself can never
transmit without first being requested to do so, and direct
message transfer between the individual slaves is not
possible. Communications occur in the half-duplex mode.
The master function cannot be transferred to another node
(single-master system).
The physical layer is RS485, thus utilising the RS485 port
built into the frequency converter. The FC protocol
supports different telegram formats:
•
A short format of 8 bytes for process data.
•
A long format of 16 bytes that also includes a
parameter channel.
•
A format used for texts.
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Design Guide
Brake resistor
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3.8.6 Network Configuration

Set the following parameters to enable the FC protocol for
the frequency converter:
Parameter number Setting
8-30 Protocol FC
8-31 Address 1–126
8-32 Baud Rate 2400–115200
8-33 Parity / Stop Bits Even parity, 1 stop bit (default)
Table 3.26 FC Protocol Parameters
3.8.7 FC Protocol Message Framing
Structure
3.8.7.1 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. This bit is set at 1
when it reaches parity. Parity is when there is an equal
number of 1s in the 8 data bits and the parity bit in total.
A stop bit completes a character, thus consisting of 11 bits
in all.
Start 0 1 2 3 4
bit
Illustration 3.44 Content of a Character
3.8.7.2 Telegram Structure
Each telegram has the following structure:
•
Start character (STX)=02 hex.
•
A byte denoting the telegram length (LGE).
•
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 3.45 Telegram Structure
5 6 7 Even Stop
Parity bit
DATA BCC
MG20N602