Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure; Telegram Length (Lge) - Danfoss VLT Design Manual

RS-485 Installation and Set...
•
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 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
7 7

7.3 FC Protocol Message Framing Structure

7.3.1 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.
Illustration 7.5

7.3.2 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.
88
®
VLT Refrigeration Drive Design Guide
Setting
FC
1 - 126
2400 - 115200
Even parity, 1 stop bit (default)
MG16G102 - VLT
Illustration 7.6

7.3.3 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).

7.3.4 Frequency Converter Address (ADR)

Two different address formats are used.
The address range of the frequency converter is either 1-31
or 1-126.
1. Address format 1-31:
Bit 7 = 0 (address format 1-31 active)
Bit 6 is not used
Bit 5 = 1: Broadcast, address bits (0-4) are not
used
Bit 5 = 0: No Broadcast
Bit 0-4 = frequency converter address 1-31
2. 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.

7.3.5 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.
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LGE = 4 + 1 + 1 = 6 bytes
LGE = 12 + 1 + 1 = 14 bytes
1)
10 +n bytes