Fc Protocol Overview; Network Configuration; Fc Protocol Message Framing Structure - Danfoss VLT AQUA Drive FC 202 Design Manual

System Integration
the RS485 communication cable away from motor and
brake resistor cables to avoid coupling of high frequency
noise from one cable to another. Normally a distance of
200 mm (8 in) is sufficient, but keeping the greatest
3 3
possible distance between the cables is recommended,
especially where cables run in parallel over long distances.
When crossing is unavoidable, the RS485 cable must cross
motor and brake resistor cables at an angle of 90°.
Min. 200 mm
90° crossing
Figure 3.44 Cable Routing

3.8.5 FC Protocol Overview

The FC protocol, also referred to as FC bus or standard bus,
is the Danfoss standard serial communication bus. It
defines an access technique according to the master-slave
principle for communications via a serial bus.
One master and a maximum of 126 slaves can be
connected to the bus. The master selects the individual
slaves via an address character in the message. A slave
itself can never transmit without first being requested to
do so, and direct message transfer between the individual
slaves is not possible. Communications occur in the half-
duplex mode.
The master function cannot be transferred to another node
(single-master system).
The physical layer is RS485, thus utilizing the RS485 port
built into the adjustable frequency drive. The FC protocol
supports different message formats:
82
®
VLT AQUA Drive FC 202
Brake resistor
Danfoss A/S © 09/2014 All rights reserved.
•
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.

3.8.6 Network Configuration

Set the following parameters to enable the FC protocol for
the adjustable frequency drive:
Parameter number Setting
8-30 Protocol FC
8-31 Address 1–126
8-32 FC Port Baud Rate 2400–115200
8-33 Parity / Stop Bits Even parity, 1 stop bit (default)
Table 3.26 FC Protocol Parameters
3.8.7 FC Protocol Message Framing
Structure
3.8.7.1 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.
Figure 3.45 Content of a Character
3.8.7.2 Message Structure
Each message has the following structure:
•
Start character (STX)=02 hex.
•
A byte denoting the message length (LGE).
•
A byte denoting the adjustable frequency drive
address (ADR).
A number of data bytes (variable, depending on the type
of message) follows.
MG20N622