Network Configuration; Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure - Danfoss VLT Compressor Drive CDS 803 Design Manual

RS485 Installation and Set-...

7.3 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 7.3 Parameters to Enable the Protocol

7.4 FC Protocol Message Framing Structure

7.4.1 Content of a Character (byte)

7 7
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 0 1
bit
Illustration 7.4 Content of a Character

7.4.2 Telegram Structure

Each telegram has the following structure:
1. Start character (STX)=02 hex.
2. A byte denoting the telegram length (LGE).
3. 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 7.5 Telegram Structure
52
VLT
Setting
FC
1–126
2400–115200
Even parity, 1 stop bit (default)
2 3 4 5 6 7
ADR DATA
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Compressor Drive CDS 803

7.4.3 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 7.4 Length of Telegrams
1) The 10 is the fixed characters, while the n is variable (depending
on the length of the text).

7.4.4 Frequency Converter Address (ADR)

Address format 1–126
•
Bit 7 = 1 (address format 1–126 active).
•
Bit 0–6 = frequency converter address 1–126.
•
Bit 0–6 = 0 broadcast.
The slave returns the address byte unchanged to the
master in the response telegram.

7.4.5 Data Control Byte (BCC)

The checksum is calculated as an XOR-function. Before the
first byte in the telegram is received, the calculated
checksum is 0.
Even Stop
Parity bit
BCC
LGE=4+1+1=6 bytes
LGE=12+1+1=14 bytes
10 1) +n bytes
MG18N202