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

RS-485 Installation and Set...

7.3 Network Connection

One or more frequency converters can be connected to a
control (or master) using the RS-485 standardised interface.
Terminal 68 is connected to the P signal (TX+, RX+), while
terminal 69 is connected to the N signal (TX-, RX-). See
illustrations in chapter 5.9.3 Earthing of Screened/Armoured
Control Cables
If more than one frequency converter is connected to a
master, use parallel connections.
7 7
Illustration 7.3 Parallel Connections
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
Illustration 7.4 Control Card Terminals
150
Design Guide
RS 232
68 69 68
+
USB
-
RS 485
39 42 50 53 54 55
Remove jumper to enable Safe Stop
12 13 18 19 27 29 32 33
Danfoss A/S © Rev. 06/2014 All rights reserved.

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, 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 8 data bits and the parity bit
in total. A stop bit completes a character, thus consisting
of 11 bits in all.
Start 0
bit
Illustration 7.5 Character (Byte)
69 68 69

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.
20 37
STX
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.
•
•
•
1) The 10 represents the fixed characters, while the "n'" is
variable (depending on the length of the text).
1 2 3 4 5 6
Start character (STX)=02 Hex
A byte denoting the telegram length (LGE)
A byte denoting the frequency converter address
(ADR)
LGE ADR DATA
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
7 Even Stop
Parity bit
BCC
1)
+n
MG20Z202