Network Configuration; Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure - Danfoss VLT FC51 Design Manual

RS-485 Installation and Set...
The physical layer is RS-485, thus utilising the RS-485 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
8.2.1 FC with Modbus RTU
The FC protocol provides access to the control word and
bus reference of the frequency converter.
The control word allows the Modbus master to control
several important functions of the frequency converter.
•
Start
•
Stop of the frequency converter in various ways:
- Coast stop
- Quick stop
- DC Brake stop
- Normal (ramp) stop
•
Reset after a fault trip
•
Run at various preset speeds
•
Run in reverse
•
Change of the active set-up
•
Control of the 2 relays built into the frequency
converter
The bus reference is commonly used for speed control. It is
also possible to access the parameters, read their values,
and where possible, write values to them. This permits a
range of control options, including controlling the setpoint
of the frequency converter when its internal PI controller is
used.

8.3 Network Configuration

8.3.1 Frequency Converter Set-up
Set the following parameters to enable the FC protocol for
the frequency converter.
Parameter 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 8.3 Network Configuration Parameters
®
VLT Micro Drive FC 51 Design Guide

8.4 FC Protocol Message Framing Structure

8.4.1 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. 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
bit
Illustration 8.4 Content of a Character

8.4.2 Telegram Structure

Each telegram has the following structure:
1.
2.
3.
A number of data bytes (variable, depending on the type
of telegram) follows.
A data control byte (BCC) completes the telegram.
STX
Illustration 8.5 Telegram Structure

8.4.3 Telegram Length (LGE)

The telegram length is the number of data bytes plus the
address byte ADR and the data control byte BCC.
4 data bytes
12 data bytes
Telegramscontaining texts
Table 8.4 Length of Telegrams
1) The 10 represents the fixed characters, while the "n'" is variable
(depending on the length of the text).
MG02K302 - Rev. 2013-12-03
0 1 2 3 4 5
Start character (STX)=02 hex
A byte denoting the telegram length (LGE)
A byte denoting the frequency converter address
(ADR)
LGE ADR DATA
LGE=4+1+1=6 bytes
LGE=12+1+1=14 bytes
1)
10 +n bytes
6 7 Even Stop
Parity bit
8
BCC
67
8