Fc With Modbus Rtu; Network Configuration; Fc Protocol Message Framing Structure; Content Of A Character (Byte) - Danfoss VLT Midi Drive FC 280 Design Manual

RS485 Installation and Set-...
The physical layer is RS485, thus utilizing 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.

5.2.2 FC with Modbus RTU

5 5
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:
-
-
-
-
•
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. Accessing the
parameters offers a range of control options, including
controlling the setpoint of the frequency converter when
its internal PI controller is used.

5.3 Network Configuration

To enable the FC protocol for the frequency converter, set
the following parameters.
Parameter
Parameter 8-30 Protocol
Parameter 8-31 Address
Parameter 8-32 Baud
Rate
Parameter 8-33 Parity /
Stop Bits
Table 5.3 Parameters to Enable the Protocol
56
®
VLT
Coast stop.
Quick stop.
DC brake stop.
Normal (ramp) stop.
Setting
FC
1–126
2400–115200
Even parity, 1 stop bit (default)
Danfoss A/S © 03/2016 All rights reserved.
Midi Drive FC 280

5.4 FC Protocol Message Framing Structure

5.4.1 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 are an equal
number of 1s in the 8 data bits and the parity bit in total.
A stop bit completes a character, consisting of 11 bits in
all.
Start 0 1
bit
Illustration 5.3 Content of a Character

5.4.2 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).
Several data bytes (variable, depending on the type of
telegram) follow.
A data control byte (BCC) completes the telegram.
STX LGE
Illustration 5.4 Telegram Structure

5.4.3 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
Telegrams containing texts
Table 5.4 Length of Telegrams
1) The 10 represents the fixed characters, while the n is variable
(depending on the length of the text).
2 3 4 5 6 7
ADR DATA
LGE=4+1+1=6 bytes
LGE=12+1+1=14 bytes
1)
10 +n bytes
Even Stop
Parity bit
BCC
MG07B102