Network Configuration; Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

RS-485 Installation and Set...
of the frequency converter when its internal PI controller is
used.

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 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 7.3

7.4 FC Protocol Message Framing Structure

7.4.1 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 0 1 2 3 4
bit
Illustration 7.3

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)
A number of data bytes (variable, depending on the type
of telegram) follows.
A data control byte (BCC) completes the telegram.
®
VLT HVAC Basic Drive Design Guide
5 6 7 Even Stop
Parity bit
®
MG18C402 - VLT is a registered Danfoss trademark
STX LGE ADR
Illustration 7.4

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
Telegramscontaining texts
Table 7.4 Length of telegrams
1)
The 10 represents 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.

7.4.6 The Data Field

The structure of data blocks depends on the type of
telegram. There are three telegram types, and the type
applies for both control telegrams (master⇒slave) and
response telegrams (slave⇒master).
The 3 types of telegram are:
Process block (PCD)
The PCD is made up of a data block of 4 bytes (2 words)
and contains:
- Control word and reference value (from master to
slave)
- Status word and present output frequency (from
slave to master)
DATA BCC
LGE=4+1+1=6 bytes
LGE=12+1+1=14 bytes
10 1) +n bytes
79
7 7