Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure; Telegram Length (Lge) - Danfoss VLT AQUA Drive FC 202 Design Manual

RS-485 Installation and Set...
To avoid potential equalising currents in the screen, earth
the cable screen via terminal 61, which is connected to the
frame via an RC-link.
61 68 69
Remove jumper to enable Safe Stop
12 13 18 19
Illustration 7.4 Control Card Terminals

7.4 FC Protocol Message Framing Structure

7.4.1 Content of a Character (byte)

Each character transferred begins with a start bit. Then
eight data bits are transferred, each 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 characters in the eight 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 7.5 Character (Byte)

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.
®
VLT AQUA Drive FC 202 Design Guide
39 42 50 53 54 55
27 29 32 33 20 37
5 6 7 Even Stop
Parity bit
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MG20Z102 - VLT is a registered Danfoss trademark
A data control byte (BCC) completes the telegram.
STX LGE ADR
Illustration 7.6 Telegram Structure

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.
•
The length of telegrams with 4 data bytes is
LGE=4+1+1=6 bytes
•
The length of telegrams with 12 data bytes is
LGE=12+1+1=14 bytes
•
The length of telegrams containing texts is 10
bytes
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)

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.

7.4.5 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.
DATA BCC
1)
+n
167
7 7