Network Configuration; Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure - Danfoss VLT HVAC Drive FC 102 Design Manual

Installation and Set-up
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 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.
7.2.1 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 a variety of preset speeds
•
Run in reverse
•
Change of the active set-up
•
Control of the two 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 PID controller
is used.
MG16C202
Design Guide

7.3 Network Configuration

7.3.1 Frequency Converter Set-up
Set the following parameters to enable the FC protocol for
the frequency converter.
Parameter Number
8-30 Protocol
8-31 Address
8-32 Baud Rate
8-33 Parity / Stop Bits
Table 7.3 FC Protocol Parameters

7.4 FC Protocol Message Framing Structure

7.4.1 Content of a Character (byte)

Each character transferred begins with a start bit. Eight
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 7.5 Example Character

7.4.2 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 7.6 Example Telegram
Danfoss A/S © Rev. 05/2014 All rights reserved.
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
7
6 7 Even Stop
Parity bit
BCC
171
7