Network Configuration; Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure - Danfoss VLT Micro Drive FC 51 Design Manual

RS485 Installation and Set-...
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.
8.2.2 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. Accessing the
parameters offers a range of control options, including
controlling the setpoint of the frequency converter when
its internal PI controller is used.
MG02K402
Design Guide

8.3 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 8.3 Parameters to Enable the Protocol

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 1 s 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:
•
•
•
Several data bytes (variable, depending on the type of
telegram) follow.
A data control byte (BCC) completes the telegram.
STX
Illustration 8.5 Telegram Structure
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Setting
FC
1–126
2400–115200
Even parity, 1 stop bit (default)
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
8
6 7 Even Stop
Parity bit
BCC
67
8