Danfoss VLT AutomationDrive FC 301 Series Design Manual page 192

RS-485 Installation and Set...
12.5 FC Protocol Overview
The FC protocol, also referred to as FC bus or Standard
bus, is the Danfoss standard serial communication bus. It
defines an access technique according to the master-
follower principle for communications via a serial bus.
One master and a maximum of 126 followers can be
connected to the bus. The master selects the individual
followers via an address character in the message. A
follower itself can never transmit without first being
requested to do so, and direct message transfer between
the individual followers 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 RS-485, thus utilizing the RS-485 port
built into the adjustable frequency drive. The FC protocol
supports different message 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
12.6 Network Configuration
12.6.1 Adjustable Frequency Drive Set-up
Set the following parameters to enable the FC protocol for
the adjustable frequency drive.
12 12
Parameter Number
8-30 Protocol
8-31 Address
8-32 FC Port Baud Rate
8-33 Parity / Stop Bits
Table 12.2 FC Protocol Parameters
190
Design Guide
Setting
Adjustable Frequency Drive
1–126
2400–115200
Even parity, 1 stop bit (default)
Rev. 2014-04-04 All rights reserved.
12.7 FC Protocol Message Framing
Structure
12.7.1 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.
Figure 12.5 Content of a Character
12.7.2 Message Structure
Each message has the following structure:
1. Start character (STX)=02 hex
2. A byte denoting the message length (LGE)
3. A byte denoting the adjustable frequency drive
address (ADR)
A number of data bytes (variable, depending on the type
of message) follows.
A data control byte (BCC) completes the message.
STX LGE ADR
Figure 12.6 Message Structure
DATA BCC
MG33BF22